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({}),
+      }),
   },
 
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