fix(git-status): address #537 review (docker workspaces, gone upstream, in-flight reset, docs)

- never inspect a repository at or inside a Docker case workspace (walk-up, scan, diff route): git would run its clean filters on the host
- a branch whose upstream was deleted and pruned reports upstreamGone and falls back to commits on no remote, instead of green
- turning the setting off during a poll releases the in-flight flag
- log.showSignature=false; reword the docs: clean filters still run
- CLAUDE.md frontend load order, changeset names git-diff
- discovery reads a bounded, sorted directory listing; leading-dash paths allowed; diff 500 redacts credentials
- keyboard focus survives the poll re-render; panel stays on screen on narrow viewports; aria-expanded visible on light skins

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JrzFKEdBLwVfu6ev2ZscJS

docs/api-reference.md

@@ -702,9 +702,9 @@ normal `caseName`/`mode`/etc. body)
 
 ## Git status
 
-`GET /api/sessions/:id/git-status` is what the bottom-bar Git indicator and its panel read (Settings → Header & Panels → Bottom bar, per-device, default off). It reports what the session's workspace has not committed or pushed. **Read-only and offline:** it never fetches, pulls, commits or writes (it runs `git status` with `--no-optional-locks`, so it does not even refresh the index), which is why `behind` is as of the last `git fetch`. The session is resolved like every session route (ownership via `findSessionOrFail`; another user's session is `404`).
+`GET /api/sessions/:id/git-status` is what the bottom-bar Git indicator and its panel read (Settings → Header & Panels → Bottom bar, per-device, default off). It reports what the session's workspace has not committed or pushed. **Read-only and offline:** it never fetches, pulls, commits or writes (it runs `git status` with `--no-optional-locks`, so it does not even refresh the index), which is why `behind` is as of the last `git fetch`. The session is resolved like every session route (ownership via `findSessionOrFail`; another user's session is `404`). A repository whose root is, or is inside, a Docker case workspace is dropped (from the walk-up, the scan below a folder, and the diff route): a container can write there, and a repository's own clean filter or signature program would run on the host. When a branch's upstream was deleted and pruned on the remote, `upstreamGone` is `true` and the unpushed list falls back to commits on no remote-tracking ref at all.
 
-`GET /api/sessions/:id/git-diff?repo=<repoRoot>&path=<path>&kind=staged|unstaged|untracked|conflicted` returns the unified diff of one file the panel lists (`{ diff, truncated, binary }`; staged is index vs HEAD, unstaged is working tree vs index, untracked is the whole file as additions). It is what opens when you click a file in the Git panel. `repo` and `path` are matched against the current status rather than trusted, so anything the status does not list is `404`. Read-only (`--no-ext-diff --no-textconv`, so repository config never runs a program), capped at 400 KB, and refused (`400`) for remote and Docker sessions.
+`GET /api/sessions/:id/git-diff?repo=<repoRoot>&path=<path>&kind=staged|unstaged|untracked|conflicted` returns the unified diff of one file the panel lists (`{ diff, truncated, binary }`; staged is index vs HEAD, unstaged is working tree vs index, untracked is the whole file as additions). It is what opens when you click a file in the Git panel. `repo` and `path` are matched against the current status rather than trusted, so anything the status does not list is `404`. Read-only: it passes `--no-ext-diff --no-textconv` (no external diff or textconv driver runs), but a repository's clean filters still run, as they do for any `git diff`, which is why a repository a container can write to is never inspected (below). Capped at 400 KB, and refused (`400`) for remote and Docker sessions; a repository at or inside a Docker case workspace is not in the status, so it is `404` here.
 
 **Which repositories.** git finds a repository by walking *up* from the session's working directory, so: