feat: add in-app self-updater (App Settings → Updates)

Update Codeman from the web UI: a "Check for updates" button queries GitHub
for the latest tagged release (git ls-remote fallback) and shows release
notes; "Update now" runs git checkout <tag> → npm install → npm run build →
restart, streaming live progress that survives the service restart.

- Release-tag channel; dirty trees auto-stashed (left for manual git stash pop)
- Cross-platform restart: systemd / launchd / manual, detected at runtime
- Updater runs detached (systemd-run --scope on Linux, setsid on macOS) so the
  restart it triggers can't kill the build mid-flight
- Build-failure rollback to the pre-update commit; boot reconcile with an
  update-id/freshness guard; 409 concurrency lock; runner staged outside the
  repo; strict tag validation; CODEMAN_DISABLE_SELF_UPDATE kill-switch
- Endpoints: GET /api/system/update/check, POST /api/system/update,
  GET /api/system/update/status

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/web/server.ts

@@ -85,6 +85,8 @@ import {
   type RespawnWiringDeps,
 } from './respawn-event-wiring.js';
 
+import { reconcileUpdateOnBoot } from './self-update.js';
+
 // Load version from package.json
 const require = createRequire(import.meta.url);
 const { version: APP_VERSION } = require('../../package.json');
@@ -1665,6 +1667,13 @@ export class WebServer extends EventEmitter {
     lifecycleLog.log({ event: 'server_started', sessionId: '*' });
     await lifecycleLog.trimIfNeeded();
 
+    // If a self-update restarted us into this process, finalize its status file
+    // (flip the persisted "restarting" marker → completed/failed based on the
+    // version we actually booted). No-op on a normal boot. See web/self-update.ts.
+    if (!this.testMode) {
+      reconcileUpdateOnBoot();
+    }
+
     // Restore mux sessions BEFORE accepting connections
     // This prevents race conditions where clients connect before state is ready
     // CRITICAL: Skip in test mode to prevent tests from picking up user sessions