feat(browser): redo file operations with Ctrl+Shift+Z

[JoeJoeflyn]

Description

Adds Finder-style redo for every undoable file operation. Undo keeps a process-wide history stack shared across windows; this adds a parallel redo stack fed by completed undos, so Ctrl+Shift+Z (and Ctrl+Y) re-applies what was just reverted:

• Trash → re-trashes the restored locations
• Move → replays the transfer with swapped endpoints, through the same collision dialog as undo
• Copy → restores the trashed copies from Trash
• Rename → replays the rename with swapped endpoints
• Put Back → rides on the UndoEntry::Copy entries restore already records, so undoing a Put Back (re-trash) can itself be redone

Two correctness rules:

• Invalidation — any new forward operation clears the redo stack (push_pending_undo), matching Finder.
• Partial replay — undo/redo can half-complete on conflicts. A completed bucket on each pending entry accumulates only items that actually applied, so a partial undo offers a redo for just the reverted portion, and a partial redo regenerates the matching undo subset. Failed operations push nothing — a failed rename undo, for example, offers no redo.

Undo and redo share one replay core (replay_move, replay_rename, replay_entry_locations, resolve_replay_collisions, finish_claimed_replay) parameterized by direction rather than duplicated per direction. Replays reuse the existing provider operations (undo_move, undo_rename, undo_copy, restore) — no new provider API.

Merge/copy-overwrite undos deliberately offer no redo: a merge undo mixes deletions and restores that no single replay operation can re-apply.

Visual evidence

screenrecording-2026-09-18_21-21-14.mp4

• target/pr-captures/redo-1-restored.png — after Ctrl+Z: todo.txt put back in the listing
• target/pr-captures/redo-2-retrashed.png — after Ctrl+Shift+Z: todo.txt re-trashed, listing back to four items

How to test

1. Trash a file (Delete), press Ctrl+Z — the file is put back; press Ctrl+Shift+Z — it is trashed again
2. Cut+paste a file to another folder, Ctrl+Z, Ctrl+Shift+Z — moves back, then forward again
3. Copy+paste, Ctrl+Z, Ctrl+Shift+Z — copy trashed, then restored
4. Rename (F2), Ctrl+Z, Ctrl+Shift+Z — old name, then new name again
5. Trash, Ctrl+Z, then rename any other file, Ctrl+Shift+Z — nothing happens: the new operation invalidated redo
6. Multi-select → cut+paste → Ctrl+Z → Skip on a conflict → Ctrl+Shift+Z redoes only the files that actually reverted

Related issue

Closes #1117