v0.12.6: fix rsync destination nesting and exclude app-internal DB dumps

Two rsync bugs found during Immich cross-drive backup testing:

Fix 3: Simplified destination path structure in runRsyncBackup.
Old SplitN logic kept "storage/immich" as a subpath, creating redundant
nesting: backups/rsync/immich/storage/immich/<data>. New logic: single
mount → rsync directly into the stack folder; multiple mounts → use
each mount's leaf dir name as subfolder (disambiguated by _N suffix).

Fix 4: Exclude app-internal DB dump files from rsync. Apps like Immich
store periodic pg_dumps in <data>/backups/*.sql.gz. The controller
already handles DB backups via pg_dump — copying them again wastes space.
Added --exclude backups/*.sql.gz/sql/dump to the rsync command.

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

controller/README.md

@@ -4,7 +4,7 @@
 
 A single, lightweight Go container that replaces Portainer + scattered systemd scripts with a unified, Hungarian-language web dashboard for managing Docker Compose stacks, backups, storage, monitoring, and notifications on customer hardware.
 
-**Current version: v0.12.5**
+**Current version: v0.12.6**
 
 ---
 
@@ -196,6 +196,10 @@ Implements the 3-2-1 backup rule by copying data to a different physical drive.
   - External mount: block if <100 MB free; warn/block at 90%/95% usage
   - System drive (same block device as `/`): require ≥10 GB free AND <90% usage to protect OS stability; allowed with a logged warning (no hard block for non-mount-point destinations)
   - Web UI `CheckBackupDestination` matches runner thresholds — no surprise divergence between UI and actual enforcement
+- **Rsync destination layout** (`runRsyncBackup`):
+  - Single mount: data goes directly into `backups/rsync/<app>/` (no extra nesting)
+  - Multiple mounts: each gets a `backups/rsync/<app>/<leaf>/` subfolder named after the mount's base directory; duplicate leaf names disambiguated with `_N` suffix
+  - DB dump files excluded: `--exclude backups/*.sql.gz`, `--exclude backups/*.sql`, `--exclude backups/*.dump` — avoids duplicating data already managed by the pg_dump layer
 - Safety guards: destination ≠ source, path-overlap check, writable check
 - **Chained execution**: cross-drive runs immediately after nightly restic backup (daily apps every night, weekly apps on Sundays) for DB/file consistency
 - Per-app concurrency lock prevents overlapping runs