v0.14.0: Per-drive backup architecture + storage path overhaul

Major refactor of backup and storage paths:

- Per-drive restic repos at <drive>/backups/primary/restic/
- Per-app DB dumps at <drive>/backups/primary/<app>/db-dumps/
- Remove global BackupDir, DBDumpDir, ResticRepo config fields
- Add SystemDataPath config (fallback for apps without HDD)
- New backup/paths.go with pure path computation helpers
- Add GetStackHDDPath to StackDataProvider interface
- Restic methods now accept repoPath as parameter
- Cross-drive backup uses new secondary path structure
- Rename storage/ to appdata/ in scripts and compose templates
- Update protected HDD paths (storage → appdata + backups)
- Simplify backup UI (remove global path displays)

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

controller/internal/stacks/delete.go

@@ -41,10 +41,10 @@ func ProtectedHDDPaths(hddPath string) map[string]bool {
 	}
 	return map[string]bool{
 		hddPath:                                true,
-		filepath.Join(hddPath, "media"):        true,
-		filepath.Join(hddPath, "storage"):      true,
-		filepath.Join(hddPath, "Dokumentumok"): true,
 		filepath.Join(hddPath, "appdata"):      true,
+		filepath.Join(hddPath, "backups"):      true,
+		filepath.Join(hddPath, "media"):        true,
+		filepath.Join(hddPath, "Dokumentumok"): true,
 	}
 }