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/RELEASE_NOTES.md

@@ -66,11 +66,11 @@ name — `file2` before `file10` — size, date or type; hidden files on request
 search that either stays in the folder you are in or looks everywhere through an on-device index
 which says how current its answer is.
 
-**Moving files around.** Copy, move, rename and delete one item or many. **Copy to…** and **Move
+**Moving files around.** Copy, move, rename and delete one item or many. **Copy to…** and **Cut
 to…** open a folder picker — volumes first, then one level at a time — and start the transfer into
 that folder without taking you out of the one you are standing in. A finished copy says
-*Copied to folder* and offers **Show**. A name that already exists asks what Paste asks instead of
-overwriting, and a batch that cannot succeed is refused as a whole rather than performed until it
+*Copied to folder* and offers **Show**. A name that already exists asks before overwriting, and a
+batch that cannot succeed is refused as a whole rather than performed until it
 hits the problem. The rows an operation produced carry a dot until you next open that folder, so
 "what did that 4 GB copy do?" has an answer even when the destination was elsewhere.