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/web/handlers.go

@@ -525,8 +525,7 @@ func (s *Server) backupsHandler(w http.ResponseWriter, r *http.Request) {
 			data["ResticPassword"] = pw
 		}
 
-		// Tároló section: DB dump directory and total size
-		data["DBDumpDir"] = s.cfg.Paths.DBDumpDir
+		// Tároló section: DB dump total size
 		var dbDumpTotalBytes int64
 		for _, f := range fullStatus.DumpFiles {
 			dbDumpTotalBytes += f.Size