feat(ui): git status indicator in the bottom bar, with a panel of uncommitted and unpushed work

Optional and per-device (showGitStatus, default off). GET /api/sessions/:id/git-status is
read-only and offline (no fetch, --no-optional-locks), skips remote and Docker sessions, caps its
lists, and single-flights concurrent polls. The toolbar indicator shows uncommitted files,
commits not pushed, or a check; clicking opens a draggable panel in the style of the Files window.

Which repositories: the enclosing one when there is one; otherwise every repository up to two
levels below the working directory (capped, skipping dot-folders and node_modules, never
following symlinks), each in a collapsible section, with the indicator summing them. A repository
that merely sits above the workspace and is the home folder or higher (a dotfiles repo) is
ignored. Git-supplied text is only ever written with textContent.

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

docs/api-reference.md

@@ -700,6 +700,27 @@ normal `caseName`/`mode`/etc. body)
   jarring than a full relaunch, and folding it into the one-shot path is
   separate work — see `docs/custom-model-endpoints-plan.md`).
 
+## 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`).
+
+**Which repositories.** git finds a repository by walking *up* from the session's working directory, so:
+
+- Inside a repository (or at its root): that one repository, whole (a subfolder reports its enclosing repo, `path` says where it is, e.g. `../..`). A nested repo below it is just an untracked folder to the outer one and is not scanned; start the session inside it to see it.
+- **Not** inside one (a folder that holds several projects): every repository found up to **two levels down**, nearest and alphabetical first, at most 12 (`reposTruncated` says when there were more). Dot-folders, `node_modules`, `dist`, `build`, `target`, `vendor`, `venv` and `__pycache__` are skipped, symlinks are never followed, and a repository's own contents are not searched. The list of repositories is re-scanned at most every 30 s; each repository's status is cached for 4 s.
+- A repository that merely sits **above** the workspace and is the home folder or higher (a dotfiles repo in `$HOME`, or `/`) is ignored: its dirty files are not this session's work. A workspace that *is* that repository's root is not ignored.
+- A worktree (whose `.git` is a file) counts as a repository. A submodule's own uncommitted files are not reported, only a changed submodule pointer.
+
+`data` is `{ state, repos, reposTruncated, checkedAt }`:
+
+- `state: 'ok'`: `repos[]`, each `{ name, path, status }` where `name` is the repository folder's name, `path` its root relative to the working directory, and `status` is:
+  `branch` (null when `detached`), `upstream`, `ahead`, `behind`, `hasRemote`, `counts` (`staged`, `unstaged`, `untracked`, `conflicted`, `uncommitted` = distinct paths, `stashes`), `files[]` (`path` relative to `repoRoot`, `origPath` for a rename, `index` and `worktree` status letters, `kind`: `staged` \| `unstaged` \| `untracked` \| `conflicted`; a file that is staged *and* modified again appears once per kind), `filesTruncated`, `unpushedCount` (exact) and `unpushed[]` (newest first: `hash`, `author`, `time` in epoch seconds, `subject`), `repoRoot`, `checkedAt`.
+- `state: 'not-a-repo'`: no repository here, above (that counts) or within two levels below.
+- `state: 'unsupported'` with `reason: 'remote' | 'docker'`: those sessions are never inspected (a Docker workspace is writable from inside its sandbox, and git here would run on the host).
+- `state: 'error'` with a short `error` (git missing, timed out, or git's first stderr line with any `user:token@` credentials redacted).
+
+Lists are capped (300 files and 50 commits per repository) while the counts stay exact. A branch with no upstream reports the commits no remote has (`HEAD --not --remotes`); a repository with no remote reports `unpushedCount: 0`, since there is nothing to push to. Concurrent polls of one folder share a single git invocation; `?fresh=1` (what the panel's Refresh button and opening the panel send) skips the short-lived caches, though it still joins a computation already running.
+
 ## CLI management
 
 Read and write the CLI registry (`docs/cli-registry.md`). Every **write** route answers `403 FORBIDDEN` while `cliManagementEnabled` is off (the default), and for a non-admin in multi-user mode. A write that would overwrite a `clis.json` which does not parse, or which has group/world permission bits, is refused with `409 CONFLICT` and a message naming the fix; the file is left untouched.