feat: comprehensive debug logging across all controller modules

Add detailed [DEBUG] logging to every controller module when
logging.level is set to "debug". Each module with stateful debug
uses SetDebug(bool) wired from main.go. Covers stacks, backup,
cloudflare, integrations, system, monitor, settings, scheduler,
web handlers, storage, metrics, API, selfupdate, and assets.

Also includes the app export/import (.fab bundles) feature from
v0.32.0 and its debug page integration.

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

controller/internal/storage/migrate_drive.go

@@ -101,6 +101,16 @@ func (tx *migrationTx) rollback() {
 // MigrateDrive performs a full drive migration, moving all apps from source to dest.
 func (dm *DriveMigrator) MigrateDrive(ctx context.Context, req DriveMigrateRequest, progress chan<- DriveMigrateProgress) error {
 	start := time.Now()
+	debug := dm.Logger != nil
+
+	dbg := func(format string, args ...interface{}) {
+		if debug {
+			dm.Logger.Printf("[DEBUG] [storage] MigrateDrive: "+format, args...)
+		}
+	}
+	_ = dbg // used below
+
+	dbg("starting drive migration: source=%s dest=%s", req.SourcePath, req.DestPath)
 
 	send := func(step, msg string, pct int) {
 		progress <- DriveMigrateProgress{
@@ -175,6 +185,14 @@ func (dm *DriveMigrator) MigrateDrive(ctx context.Context, req DriveMigrateReque
 		}
 	}
 
+	dbg("found %d apps on source drive: %v", len(appsToMigrate), func() []string {
+		names := make([]string, len(appsToMigrate))
+		for i, a := range appsToMigrate {
+			names[i] = a.Name
+		}
+		return names
+	}())
+
 	if len(appsToMigrate) == 0 {
 		return fail("A forrás meghajtón nincs telepített alkalmazás", fmt.Errorf("no apps on source"))
 	}
@@ -230,6 +248,7 @@ func (dm *DriveMigrator) MigrateDrive(ctx context.Context, req DriveMigrateReque
 		)
 	}
 
+	dbg("estimated data: %s (%d bytes), free on dest: %s (%d bytes)", bytesHuman(totalBytes), totalBytes, bytesHuman(freeBytes), freeBytes)
 	dm.Logger.Printf("[INFO] Drive migration: %s (%s) → %s (%s), %d apps, ~%s data",
 		req.SourcePath, srcLabel, req.DestPath, dstLabel, len(appsToMigrate), bytesHuman(totalBytes))
 
@@ -330,11 +349,13 @@ func (dm *DriveMigrator) MigrateDrive(ctx context.Context, req DriveMigrateReque
 
 	if err := rsyncCmd.Wait(); err != nil {
 		stderrWg.Wait()
+		dbg("rsync failed after %s: %v — stderr: %s", time.Since(start).Round(time.Second), err, stderrBuf.String())
 		send("rolling_back", "rsync sikertelen, visszagörgetés...", 0)
 		tx.rollback()
 		return fail("Adatmásolás sikertelen", fmt.Errorf("rsync failed: %w — %s", err, stderrBuf.String()))
 	}
 	stderrWg.Wait()
+	dbg("rsync completed in %s", time.Since(start).Round(time.Second))
 
 	// --- Step 3: Verify copy ---
 	send("verifying", "Másolat ellenőrzése...", 62)
@@ -351,6 +372,7 @@ func (dm *DriveMigrator) MigrateDrive(ctx context.Context, req DriveMigrateReque
 	// --- Step 4: Update all app configs ---
 	send("configuring", "Konfiguráció frissítése...", 65)
 
+	dbg("updating HDD_PATH for %d apps", len(appsToMigrate))
 	var configuredApps []string
 	for i, app := range appsToMigrate {
 		// Guard: verify app still exists