controller: config-apply self-restart + manual restart button (A)

POST /api/config/apply now takes effect via a graceful SELF-RESTART instead of
logging "restart needed" and leaving stale in-process singletons (the CF client
is built once at startup, so a rotated Cloudflare token never applied until a
manual LXC restart). Container is restart:unless-stopped, so a clean os.Exit(0)
auto-restarts with fresh config.

- New gracefulSelfRestart helper behind an injectable Restarter seam (Router.restart
  + SetRestarter) so the exit is unit-testable.
- configApply: no-op guard (byte-identical re-push → no write, no restart), else
  write → 200 (flushed) → restart. Removed stale "restart needed" wording.
- Removed the dead OnConfigApplied hook (Phase-1-retired infra-backup push; the
  self-restart reloads everything and a fresh report is pushed on startup).
- New POST /api/selfrestart (auth+CSRF via /api/ mount) + "Vezérlő újraindítása"
  settings button: confirm → POST → poll GET / every 2s → reload.
- Tests: changed→restart once; identical→not called (companion); invalid→not called;
  selfrestart→restart once.

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

controller/cmd/controller/main.go

@@ -573,12 +573,6 @@ func main() {
 
 	// --- Initialize API router ---
 	apiRouter := api.NewRouter(cfg, *configPath, sett, stackMgr, syncer, cpuCollector, backupMgr, metricsStore, updater, notifier, logger)
-	if hubPusher != nil {
-		apiRouter.OnConfigApplied = func() {
-			// Infra backup push is now the host agent's responsibility; the controller
-			// only refreshes the Hub report after a config apply.
-		}
-	}
 	if assetsSyncer != nil {
 		apiRouter.SetAssetsSyncer(assetsSyncer)
 	}