feat(controller): Hub asset syncer for logos and screenshots

Add internal/assets package that downloads and caches app assets from
Hub API with SHA-256 change detection. Assets resolve from synced cache
first, falling back to baked-in directory. Daily sync schedule +
on-demand POST /api/assets/sync endpoint.

Config: assets.sync_enabled + assets.sync_schedule (default 05:00)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

controller/cmd/controller/main.go

@@ -16,6 +16,7 @@ import (
 	"strings"
 
 	"gitea.dooplex.hu/admin/felhom-controller/internal/api"
+	"gitea.dooplex.hu/admin/felhom-controller/internal/assets"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/backup"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/config"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/metrics"
@@ -425,6 +426,23 @@ func main() {
 		return storageWatchdog.Check(ctx)
 	})
 
+	// --- Asset syncer (download from Hub) ---
+	var assetsSyncer *assets.Syncer
+	if cfg.Hub.Enabled && cfg.Assets.SyncEnabled && cfg.Hub.URL != "" && cfg.Hub.APIKey != "" {
+		assetsDir := filepath.Join(cfg.Paths.DataDir, "assets")
+		assetsSyncer = assets.New(cfg.Hub.URL, cfg.Hub.APIKey, assetsDir, "/usr/share/felhom/assets", logger)
+		go func() {
+			time.Sleep(10 * time.Second)
+			if err := assetsSyncer.Sync(ctx); err != nil {
+				logger.Printf("[WARN] Initial asset sync failed: %v", err)
+			}
+		}()
+		sched.Daily("asset-sync", cfg.Assets.SyncSchedule, func(ctx context.Context) error {
+			return assetsSyncer.Sync(ctx)
+		})
+		logger.Printf("[INFO] Asset sync enabled (daily at %s from Hub)", cfg.Assets.SyncSchedule)
+	}
+
 	sched.Start(ctx)
 	defer sched.Stop()
 
@@ -552,10 +570,16 @@ func main() {
 			pushInfraBackup(cfg, sett, stackProv, hubPusher, logger)
 		}
 	}
+	if assetsSyncer != nil {
+		apiRouter.SetAssetsSyncer(assetsSyncer)
+	}
 
 	// --- Initialize web server ---
 	webServer := web.NewServer(cfg, stackMgr, cpuCollector, backupMgr, crossDriveRunner, sched, sett, alertMgr, notifier, updater, logger, Version)
 	webServer.SetStorageWatchdog(storageWatchdog)
+	if assetsSyncer != nil {
+		webServer.SetAssetsSyncer(assetsSyncer)
+	}
 	if hubPusher != nil {
 		webServer.SetHubPushStatus(func() web.HubPushStatusData {
 			s := hubPusher.GetStatus()