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/configs/controller.yaml.example

@@ -29,8 +29,7 @@ infrastructure:
 paths:
   stacks_dir: "/opt/docker/stacks"     # Where compose files live
   data_dir: "/opt/docker/felhom-controller/data"
-  backup_dir: "/srv/backups"
-  db_dump_dir: "/srv/backups/db-dumps"
+  system_data_path: "/mnt/sys_drive"   # NVMe/system drive mount — fallback for apps without HDD
   hdd_path: ""                         # DEPRECATED: use Settings > Adattárolók instead. Fallback only for auto-discovery.
 
 # --- System ---
@@ -63,9 +62,12 @@ stacks:
   compose_command: ""
 
 # --- Backup ---
+# Per-drive backup paths are computed automatically:
+#   <drive>/backups/primary/restic/       — restic repo per drive
+#   <drive>/backups/primary/<app>/db-dumps/ — DB dumps per app
+#   <drive>/backups/secondary/            — cross-drive rsync + restic
 backup:
   enabled: true
-  restic_repo: "/srv/backups/restic-repo"
   restic_password_file: "/opt/docker/felhom-controller/data/restic-password"
   db_dump_schedule: "02:30"
   restic_schedule: "03:00"