feat(updates): auto-apply and self-restart on new dashboard versions

Adds POST /api/updates/apply (pull, rebuild, restart) plus an "Update now"
button and hourly auto-check in the UI, for checkouts that are safely
fast-forwardable. Reintroduces self-restart (previously removed in edc25ca
for cross-environment reliability concerns) per explicit user request.

client/src/lib/api.ts

@@ -557,6 +557,23 @@ export const api = {
         method: "POST",
         body: JSON.stringify({}),
       }),
+    /**
+     * POST /api/updates/apply - fast-forward, rebuild, and restart.
+     *
+     * Only acts when the checkout is fast-forwardable (`tracking_canonical`
+     * or `fork_or_diverged_tracking`); a 409 response means it declined
+     * (`applied: false`, `reason` explains why). On success the server
+     * restarts itself right after responding, so the caller should poll
+     * `status()` until it answers again rather than expect the connection
+     * to outlive the call.
+     *
+     * @returns {@link UpdateStatusPayload} with `applied` set.
+     */
+    apply: () =>
+      request<UpdateStatusPayload>("/updates/apply", {
+        method: "POST",
+        body: JSON.stringify({}),
+      }),
   },
 
   // ──────────────────────────────── Stats API ────────────────────────────────

client/src/lib/types.ts

@@ -1275,6 +1275,14 @@ export interface UpdateStatusPayload {
   /** Set instead of a normal result when the remote fetch itself failed
    *  (e.g. offline) - the message text explains it in user-facing terms. */
   fetch_error?: string;
+  /** Present only on the response from `POST /api/updates/apply` - true once
+   *  the checkout was fast-forwarded and rebuilt (the process is about to
+   *  restart itself). Absent from `status`/`check` responses. */
+  applied?: boolean;
+  /** Set alongside `applied: false` on an `/apply` response that declined to
+   *  act - `"up_to_date"` or `"not_fast_forwardable"` (feature branch /
+   *  detached HEAD, where there's no safe automatic move). */
+  reason?: "up_to_date" | "not_fast_forwardable";
 }
 
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