Test the interface as a user sees it, and let a debug build tell on itself

Fifteen rendering tests across four files are the first tests in this project that compose a screen,
and they cover the claims that used to be prose only: the app bar's star exists where there is a folder
to star and says Add or Remove according to the state, the selection bar offers Rename to several files
and Details only to one, the batch dialog spells out the names it will produce and refuses a collision
with the file named, the shared name dialog refuses a slash while it is typed, and a favourite that has
gone says "Folder not found" rather than showing a path that is not there. They run on the JVM through
Robolectric - the Compose test artifacts plus the test manifest - so they belong to the same verify.sh
gate as everything else instead of needing a device: 386 tests in total.

Writing them turned up one behaviour worth recording. The batch dialog continues the folder's series by
default, so a collision cannot be shown unless the start number is forced back to 1 - which is precisely
why the feature works in practice, and now also why two of these tests set the field explicitly.

The debug build now enables StrictMode (disk reads and writes, network, leaked closables; logged, not
fatal) and attaches LeakCanary. A file manager is the worst possible app for a blocking disk read on the
main thread, and a debug build is the last place where noticing it is still cheap. Logging rather than a
crash is deliberate: turning a slow screen into a crash on someone's phone is the worse trade. The flag
is read from the manifest, not from BuildConfig, which this build does not generate.

Performance has a number for the first time, and it immediately paid for itself. tools/measure-startup.sh
takes cold start with `am start -W` - median of several runs, one warm-up discarded because the first
launch after an install pays for dexopt - and docs/PERFORMANCE.md records 1814 ms over five runs, in the
debug build, which is the slow case by construction. StrictMode's first run then produced five violations
against that number: 492 ms resolving `app.cacheDir` inside the view-model factory, 397 ms reading free
space with StatFs for every volume inside refresh(), 477 ms of the platform loading its own typefaces,
and two 54 ms OEM font hooks. That is about 1.5 s of main-thread disk I/O in a 1.8 s start, of which
~0.9 s is ours and mechanical to move. Neither of ours is fixed here on purpose: the numbers and the two
fixes are recorded in PERFORMANCE.md, and they are the first items of the speed work.

What is not measured is stated in the same file rather than left to be assumed: folder open at 1 000 /
5 000 / 20 000 files, thumbnail paint while scrolling, and keystroke-to-result all need a `:benchmark`
module and a profileable build under the release package id, and this device waits for a confirmation
dialog on the first install of a new package id. The module is deliberately absent instead of
half-configured: build wiring nobody can run is worse than a recorded gap.

Gate green (map current, detekt, 386 tests, lint), and CHANGELOG, README, AGENTS.md, ROADMAP,
PERFORMANCE.md, EDGE_CASE_TESTING and the regenerated map carry it.

docs/EDGE_CASE_TESTING.md

@@ -264,6 +264,9 @@ row's wording and the message are the same strings those tests assert.
   opens the row instead of selecting it. Driving it manually on the API 35 AVD then paid for the
   caution: the compress/extract pass below found the selection bar clipping its own actions. The
   archive engine itself is covered by end-to-end JVM tests, including a zip-slip archive.
+- **Folder open, thumbnail paint and search timings.** Only cold start has been measured — see
+  [PERFORMANCE](PERFORMANCE.md), which also records why the rest needs a benchmark module and a
+  profileable build, and why that module does not exist yet.
 - **The SAF folder-picker round trip.** Driving the system picker and granting a tree was
   not attempted; the code path is unit-tested against a stand-in `DocumentsProvider`.
 - **Image viewer and thumbnails.** Verified on the AVD in M4/M5; not repeated on the phone.