feat(git): a Fetch button in the Git status header, and an interval for it app-wide and per case

Fetch is the only git command Codeman runs that writes, and the only one that runs a
repository's own fetch-post hook, so it stays behind a click and off by default. The Git
status window's header row gains Fetch; App Settings -> Bottom bar gains the switch and
the interval, synced because the scheduler acts on them, and Session Options -> Git
overrides both per case. The scheduler reads settings fresh each tick, times the interval
from the start of a run, never overlaps runs, and re-checks the Docker and remote rules
every tick before any git runs. Nothing but remote-tracking refs moves: HEAD, the index
and the working tree are proven unchanged against real git while origin/main advances.

Tests: src/git-fetch.ts and the scheduler, the per-case settings route, the synced/display
setting split, the two new i18n rows, and the Fetch block of the Git status browser suite.

docs/api-reference.md

@@ -1152,7 +1152,7 @@ Admin only in multi-user mode (`403`), like `POST /api/cases/link`: it writes ou
 
 ## 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`). 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 does not exist on the remote (deleted and pruned, or never pushed, as after cloning an empty repository and committing), `upstreamGone` is `true` and the unpushed list falls back to commits on no remote-tracking ref at all.
+`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 panel's Fetch button is a separate route, below. 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 does not exist on the remote (deleted and pruned, or never pushed, as after cloning an empty repository and committing), `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: 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.
 
@@ -1175,6 +1175,12 @@ Both routes accept two optional query parameters, which the UI sends from its pe
 
 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.
 
+`POST /api/sessions/:id/git-fetch` is the panel's **Fetch** button: one `git fetch --quiet` per repository the panel would show, through the same resolver so the two cannot disagree about which repositories belong to a workspace, with the same `maxRepos` and `timeout` clamps. It is the only git command Codeman runs that writes, and it writes remote-tracking refs only — nothing commits, checks out, merges or touches the working tree, so an agent working in the same repository is not disturbed. It runs on that click, or on the interval below and never otherwise, and `git fetch` is exactly the command that runs a repository's own `fetch-post` hook, which is why nothing runs on a timer until you opt in, and why a repository at or inside a Docker case workspace is refused before any git runs. Remote and Docker sessions answer `state: 'unsupported'` like the status route. Bounded: 4 repositories at a time, one spawn per repository with the same per-command timeout, `GIT_TERMINAL_PROMPT=0` plus BatchMode ssh so a repository that needs a login fails fast instead of hanging the request on an invisible prompt — Codeman supplies no credentials, so a repository your own git is already signed in to works because that is your existing setup.
+
+`data` is `{ state, repos, reposTruncated, repoLimit, fetchedAt }`, `repos[]` each `{ name, path, ok }` and, when it failed, `failure` (`{ code, message, stderr }`: the codes as in the clone failures, plus `NO_REMOTE`). A repository that could not be fetched keeps its row rather than being dropped. The panel shows the result under its list and then re-reads, so `behind` reflects what this fetch brought.
+
+The interval is two **synced** settings in `PUT /api/settings` (`src/git-fetch-scheduler.ts`): `gitFetchEnabled` (default `false`) and `gitFetchIntervalSeconds` (30 to 3600, default 300, the gap between runs timed from the start of a run so a slow repository does not push the next one out). Synced, not per-device, because the server is what acts on them; the scheduler reads them fresh on each 15 s tick, so a change works without a restart. A case can override both, and the override wins even while the app-wide switch is off: `POST /api/sessions/:id/git-fetch-settings` takes `{ "enabled": true | false | null, "intervalSeconds": number | null }` — `null` on a field clears that half so the app value applies again, a field left out of the body leaves the other half as it was — is `400 INVALID_INPUT` for a remote or Docker session, and answers `200` with `{ gitFetchSettings: { enabled, intervalSeconds } }` where `null` means the case follows the app. What the last run did rides the session state as `gitFetch` (`{ ranAt, trigger, state, repos, failed, firstFailure? }`, `trigger` is `click` or `interval`), on the existing `SessionUpdated` event: no new event. Remote and Docker cases are never fetched on a timer, and the Docker rule is re-checked against the CURRENT Docker roots every tick.
+
 ## Git worktrees of a case
 
 A local case whose folder is the top of a git repository can keep **worktrees** at `<case>/.claude/worktrees/<name>`, each on its own branch, so several agents on one repository never share a checkout. This is the layout Claude Code's own `claude --worktree <name>` uses (branch `worktree-<name>`), so either tool finds the other's worktrees. Remote (SSH) and Docker cases are refused with `400 INVALID_INPUT` before git runs, and so is a local case whose folder is at or inside a Docker case workspace: `git worktree add` runs the repository's post-checkout hook and checkout filters on this machine, and a container can write there. A case folder that is not a repository, is a bare repository, or sits below the repository's top level is `400` too. The case resolves the way quick-start resolves it (a linked case is admin-only in multi-user mode, everything else is the caller's own case space; another user's case is `404`), and a case folder on a mount that does not answer is `422 OPERATION_FAILED`, never `404`.