Rename a whole batch at once, numbered on from the folder's own series

Selecting more than one file and choosing Rename now opens a pattern dialog rather than the
single-file one: a name, the number to start at, and a live preview of the names it will produce.
The number is the part that makes the feature worth having. A batch rename that always starts at 1
is useless the second time it is used, because the first batch already owns 1 to 12, so the dialog
reads the names already in the folder and starts at the highest "base (n)" it finds: a folder
holding "series (1)" and "series (2)" makes the next batch start at 3, which is the market survey's
most-helpful complaint answered exactly ("if I later find another group of photos which I want to
continue the batch naming with 'Ice (3)...'"). Three rules in core/BatchRename are decisions rather
than defaults, and are written down as such: the extension is kept per file, so a mixed batch of
.jpg and .png keeps each file's own; the series is counted across extensions, because "Holiday
(9).png" making the next number 10 is one series while "Holiday (10).jpg" beside "Holiday (1).png"
is two; and it continues from the highest number rather than from the first gap, because someone
renaming a second batch is carrying a series on rather than filling in the holes of one, with the
start number theirs to type where a gap matters more.

The batch is planned in full before a single file moves, and the plan has three answers and
deliberately no fourth: Ready, Blocked (naming the target that is already in the folder) or
NothingToDo. A batch that renamed nine files of twelve and then stopped would leave the user to work
out which nine and to guess whether the last three crashed or were skipped, so a collision refuses
the whole batch, the dialog names the file in the way and disables its button as the name is typed,
and a chain is declined outright - "a.txt" taking "a (1).txt" while "a (1).txt" is itself in the
batch would need the files shuffled through temporary names. Every rename still goes through the
same FileOperations.rename a single rename uses, so the refusal to overwrite anything is the same
one, and the successful renames are collected into the single Undo.Relocate step that already
existed: a feature that touches twelve files at once owes the user one tap back. The action bar now
offers Rename to any selection, since which of the two dialogs a tap means is described by the
dialog that opens rather than by the bar; Details stays single, because "the details" of twelve
files is not a screen.

Writing it turned up a quieter bug in the rename that was already there. rename(path,
"notes/final.txt") built a child path, which resolves into the subfolder rather than alongside the
file, so a name containing a separator moved the file instead of renaming it and nothing in the
dialog or the listing showed that anything had happened. Both rename paths now refuse a name that is
not one path segment (core/FileNames.isUsableName), and the dialog says which rule it is while it is
typed, which is where the user can still do something about it.

Twenty new core tests (BatchRenameTest, FileNamesTest) and six through the view model, 350 JVM
tests in total, lint clean. Verified by driving it on the phone against a folder that already held
"series (1).txt" and "series (2).txt": with three files selected and "series" typed in, Start at
moved to 3 on its own and the preview listed "series (3).txt, series (4).txt, series (5).txt";
afterwards the folder held all five series files, each file's contents having travelled with its
rename and the two originals untouched, and the snackbar's Undo put a later batch of three back in
one step. The collision and the slash were driven the same way - the file in the way named with the
button disabled, and "A name cannot contain a slash" - and the scratch folder was removed from the
device afterwards. CHANGELOG, ROADMAP (M14), COMPETITIVE_ANALYSIS (the gap moves from candidate to
closed), STORE_LISTING and EDGE_CASE_TESTING carry the feature, its decisions and the pass itself;
two tooling notes went into the last of them, that "adb input text" does not deliver a slash and
that the dialog lifts once the keyboard appears.

docs/ROADMAP.md

@@ -1,6 +1,6 @@
 # Roadmap
 
-File Manager is built against a fixed milestone plan (**M0–M10**). This file is the
+File Manager is built against a fixed milestone plan (**M0–M14**). This file is the
 single source of truth for what is done and what remains.
 
 Legend: ✅ done · 🚧 in progress · ⏳ not started · 💡 candidate (proposed, not scheduled)
@@ -23,7 +23,7 @@ Legend: ✅ done · 🚧 in progress · ⏳ not started · 💡 candidate (propo
 | M11 | Library views | ✅ | A **Libraries** section on the root screen — Images, Videos, Audio, Documents, Archives, Recent — each row carrying how many files the index knows of that kind, each opening an ordinary listing (thumbnails, sort, multi-select, details, the existing viewers) answered from the index instead of from a directory. `core/FileCategory` groups `FileKind`s and is asserted to leave `DIRECTORY`, `APK` and `OTHER` out deliberately; `SearchIndex` gained `byKind`/`recent`/`kindCounts`, and SQLite schema **v3** adds the derived `kind` column — the migration rebuilds the table *and* drops the volume stamps, because a stamp whose rows have gone would make the next search trust an empty index. A library obeys the indexed search's own two rules: the answer comes first with the walk behind it, and every row is confirmed against the filesystem before it is shown. Not included, and recorded in the CHANGELOG as decisions rather than omissions: Downloads and New files, and restoring a library across process death. **308 JVM tests** (19 added here) |
 | M12 | Duplicate finder | ✅ | ***Find duplicates*** **in the overflow.** Three passes, cheapest first: **size** (the index's `duplicateCandidates` query — one query and no reading at all), **the first 64 KB** of every candidate (a filter that may only rule files *out*), and the **whole file** to confirm (`domain/DuplicateFinder`, SHA-256, cancellable between files and between read buffers). Groups are ordered by reclaimable space; each header states the copies and what they cost; every row carries its folder, because identical names with no paths are unactionable; and **nothing is preselected** — the delete is the app's ordinary one, through the trash and the undo snackbar. A file that cannot be read is counted and reported rather than skipped, and the empty state says how many files were compared — or that the index has never run and there was nothing to compare. **323 JVM tests** (15 added). Verified on the Xiaomi phone against four genuine groups in its own storage; the delete was deliberately not pressed on a device that is not ours — see [EDGE_CASE_TESTING](EDGE_CASE_TESTING.md) |
 | M13 | Video thumbnails | ✅ | A video row shows **a frame of the video** instead of a film icon: images and videos take the same path through Coil, with the video request asking for a frame a second in. One dependency — `coil-video` at the Coil version already pinned, whose POM adds only coil-core/stdlib/core-ktx — the platform's own `MediaMetadataRetriever` behind it, **no new permission** (no `READ_MEDIA_VIDEO`), and the decoder registered **explicitly** against an `ImageLoader` in `FileManagerApplication` — because R8 strips `coil-video`'s ServiceLoader entry from a release build, which would otherwise have left frames decoding in debug and quietly falling back to icons for real users. A decode that fails settles on the icon rather than an empty square. Verified on the phone against two purpose-made clips and a real video of the device's own, with the demo library's stand-ins falling back as intended, and **re-verified on the release APK**. **324 JVM tests** |
-
+| M14 | Batch rename with sequence continuation | ✅ | Selecting more than one file and choosing Rename opens a **pattern** dialog: a name, a start number, and a live preview of the names it will produce. `core/BatchRename` plans the whole batch before a single file moves and returns one of three answers — **Ready**, **Blocked** (naming the target the folder already holds) or **NothingToDo** — with the deliberate absence of a fourth: a batch that renamed nine of twelve and stopped would leave the user to work out which nine. The numbering **continues the folder's own series** `nextNumber` from the highest `base (n)` it finds, which is the market survey's most-helpful complaint answered by name; the extension is kept per file, the series is counted across extensions, and continuing beats filling the first gap. `SelectionBar` now offers Rename to any selection (one file keeps the name dialog, several get the pattern one), and the batch's renames are **one** `Undo.Relocate` step. The same commit hardens the single rename: `core/FileNames.isUsableName` refuses a name that is not one path segment, because `notes/final.txt` was being resolved as a path and **moved** the file instead of renaming it. **350 JVM tests** (26 added) |
 ## Key decisions
 
 | Decision | Choice | Rationale |
@@ -47,7 +47,8 @@ Legend: ✅ done · 🚧 in progress · ⏳ not started · 💡 candidate (propo
 
 A survey of the market leader (its features, and what its users praise and complain about) is in
 [COMPETITIVE_ANALYSIS](COMPETITIVE_ANALYSIS.md). Its gaps that cost **no** new permission are
-listed there as 💡 candidates. **Category libraries were the first of them and are now M11, and the
-duplicate finder the second (M12)**; the rest — batch rename with sequence continuation, bookmarks,
-and the post-paste "copy again" / "return to source folder" — are proposals, not scheduled work, and
-adding one is a roadmap decision rather than a side effect of reading that document.
+listed there as 💡 candidates. **Category libraries were the first of them and are now M11, the
+duplicate finder the second (M12) and batch rename with sequence continuation the third (M14)**; the
+rest — bookmarks, and the post-paste "copy again" / "return to source folder" — are proposals, not
+scheduled work, and adding one is a roadmap decision rather than a side effect of reading that
+document.