Make Copy to… and Cut to… the selection bar's actions

The selection bar offered Copy and Move, which only filled an in-app clipboard; the
destination picker then lived behind an overflow menu, and Paste in the top bar. That
made a copy a two-step detour through another folder - the thing M16's picker exists to
avoid.

- The bar's two verbs are now Copy to… and Cut to…, both opening the destination picker.
- The clipboard state, Paste here, and the overflow's duplicate Copy to… / Move to… are
  removed. The picker's cut title and confirm are Cut to… / Cut here.
- A copy still keeps the selection for a second destination; a cut clears it. Conflicts
  still ask before overwriting, naming the picked folder.
- Five clipboard tests are removed; the mark, restart and undo tests now use the picker.
  BrowserTopBar's search and overflow sections are extracted so its two new detekt
  findings are fixed rather than baselined.

Driven on the Xiaomi phone: Copy to… copied 120 x 16 MB through Internal storage ->
AADemo -> Target and reported Copied 121 items to Target; Cut to… moved file001.bin and
offered Undo; a name in the way raised Items already exist here; the top-bar overflow
has no Paste. The foreground-service video was re-recorded against the new bar at 16.1 s.

Verified: ./tools/verify.sh green, the code map current, 426 unit tests pass, and the
video decodes as H.264 1080x2400 with no audio.

docs/COMPETITIVE_ANALYSIS.md

@@ -309,7 +309,7 @@ requested feature in the market leader, and the permission line is a claim it ca
 | Duplicate finder | **No** | Explicitly requested, with an offer to pay. Pure local computation over a listing we can already do |
 | Batch rename, including continuing an existing numbering sequence | **No** | **Closed in M14.** Several files are renamed to one name with a number after each, and the numbering continues the folder's own series, so the "Ice (3), Ice (4)" wish from the top complainant is what the dialog now defaults to |
 | Bookmarks | **No** | **Closed in M15.** A star on any folder puts it in **Favourites** on the home screen, above the libraries; a folder that has gone is kept and marked rather than dropped |
-| "Copy again" / "Return to source folder" after a paste | **No** | **Closed as superseded.** Both exist because their flow makes you leave the source folder to paste; [ROADMAP](ROADMAP.md) specifies **Copy to… / Move to… (M16)** instead, which never leaves the source — so the selection is still there for the next destination and there is no "back to source" to offer |
+| "Copy again" / "Return to source folder" after a paste | **No** | **Closed as superseded.** Both exist because their flow makes you leave the source folder to paste; [ROADMAP](ROADMAP.md) specifies **Copy to… / Cut to… (M16)** instead, which never leaves the source — so the selection is still there for the next destination and there is no "back to source" to offer |
 | New-file dot after an operation | **No** | Their 3.6.5. Cheap, and it answers "what did that 4 GB copy just do?" |
 | Date-format setting | **No** | We deliberately leave the timestamp pattern unlocalised (README); a *user setting* is a different thing |
 | Music-player engine switch, video gesture toggle | **No** | Deep settings; low priority for a first release |
@@ -357,7 +357,7 @@ In the ROADMAP's own vocabulary (💡 = candidate, proposed, not scheduled; ✅
    Ice (2)" case that the top complainant names.
 4. ✅ **Bookmarks** — shipped as **M15**. ~~💡 "Return to source folder" and "Copy again" after a
    paste remain~~ — **closed as superseded**: both are workarounds for having to leave the source folder
-   to paste, and **Copy to… / Move to…** ([ROADMAP](ROADMAP.md), M16) removes that constraint, so the
+   to paste, and **Copy to… / Cut to…** ([ROADMAP](ROADMAP.md), M16) removes that constraint, so the
    selection is still there for the next destination and there is no "back to source" to offer.
 5. 💡 **Highlight files changed by an operation.** Their 3.6.5; answers an obvious question.
 6. **Thumbnail hardening before the next release**: register an explicit Coil `ImageLoader` with a