v0.51.0: offsite-backup UI (felhom-pbs DR) + Model-A double-nest fix

- Backups page: whole-guest backup shown as real DR — target label "Biztonsági szerver –
  külön hardver (PBS)"; app-data "Távoli mentés" card now reflects the PBS offsite tier
  (guestBackupView.Offsite) instead of "nincs beállítva".
- Model-A double-nest fix: appbackup path helpers take a felhom-data NAMESPACE ROOT (no
  internal felhom-data join); backup.Manager.namespaceRoot/AppNamespaceRoot resolve
  HDD-vs-systemDataPath provenance so a drive-resident app's backups land single-nested
  (<drive>/backups/... on the guest = <drive>/felhom-data/backups/... on the host) instead
  of .../felhom-data/felhom-data/.... Writes, deletion (GetStackBackupData/RemoveStack/
  ProtectedHDDPaths), wipe-warning scan, and export updated coherently; legacy double-nest
  dirs kept protected. New appbackup test asserts no doubled segment.

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

controller/internal/backup/backup.go

@@ -93,6 +93,26 @@ func (m *Manager) GetAppDrivePath(stackName string) string {
 	return m.systemDataPath
 }
 
+// namespaceRoot maps an app's drive path to its felhom-data namespace ROOT (the dir that directly
+// holds backups/ and appdata/). A drive-resident app's in-guest mount IS the namespace already
+// (Model A, slice 10 — the agent binds <drive>/felhom-data onto the guest mountpoint), so it is used
+// as-is; only the SSD-only system-data fallback gets the felhom-data subdir appended. This is what
+// keeps a drive-resident app's backups single-nested instead of .../felhom-data/felhom-data/... .
+func (m *Manager) namespaceRoot(drivePath string) string {
+	return NamespaceRoot(drivePath, drivePath != m.systemDataPath)
+}
+
+// AppNamespaceRoot returns the felhom-data namespace root for a stack's keep-side backups, resolving
+// HDD-vs-system provenance internally. For callers outside this package that only know the stack
+// name (e.g. the API router) so they don't double-nest the felhom-data segment.
+func (m *Manager) AppNamespaceRoot(stackName string) string {
+	drivePath := m.GetAppDrivePath(stackName)
+	if drivePath == "" {
+		return ""
+	}
+	return m.namespaceRoot(drivePath)
+}
+
 // groupStacksByDrive groups deployed stacks by their home drive path.
 func (m *Manager) groupStacksByDrive() map[string][]StackSummary {
 	if m.stackProvider == nil {
@@ -170,7 +190,7 @@ func (m *Manager) runDBDumpsInternal(ctx context.Context) error {
 			continue
 		}
 
-		dumpDir := AppDBDumpPath(drivePath, db.StackName)
+		dumpDir := AppDBDumpPath(m.namespaceRoot(drivePath), db.StackName)
 
 		result := DumpOne(ctx, db, dumpDir, m.logger, m.isDebug())
 		results = append(results, result)
@@ -239,7 +259,7 @@ func (m *Manager) DumpAppVolumes(stackName string) error {
 		return fmt.Errorf("cannot determine drive path for %s", stackName)
 	}
 
-	dumpDir := AppVolumeDumpPath(drivePath, stackName)
+	dumpDir := AppVolumeDumpPath(m.namespaceRoot(drivePath), stackName)
 	if err := os.MkdirAll(dumpDir, 0755); err != nil {
 		return fmt.Errorf("creating volume dump dir: %w", err)
 	}
@@ -395,7 +415,7 @@ func (m *Manager) DumpStackDB(ctx context.Context, stackName string) error {
 	if drivePath == "" || !filepath.IsAbs(drivePath) {
 		return fmt.Errorf("cannot determine absolute drive path for %s (systemDataPath not configured?)", stackName)
 	}
-	dumpDir := AppDBDumpPath(drivePath, stackName)
+	dumpDir := AppDBDumpPath(m.namespaceRoot(drivePath), stackName)
 
 	m.logger.Printf("[INFO] [backup] Running pre-backup DB dump for %s (%d database(s)) → %s", stackName, len(stackDBs), dumpDir)
 
@@ -428,7 +448,7 @@ func (m *Manager) listAllDumpFiles() []DumpFileInfo {
 	var allFiles []DumpFileInfo
 	for drive, stacks := range m.groupStacksByDrive() {
 		for _, stack := range stacks {
-			dumpDir := AppDBDumpPath(drive, stack.Name)
+			dumpDir := AppDBDumpPath(m.namespaceRoot(drive), stack.Name)
 			if files, err := ListDumpFiles(dumpDir); err == nil {
 				allFiles = append(allFiles, files...)
 			}