fix: fix services accessig directly to localstorage

Prevent services accessing directly to localstorage and prefer using an astraction layer
to expose full blob. The abstraction layer (dedup services) will cover backend storage
election (local, s3, ...), encryption, etc

This change permit audio_metadata_service, media_metadaa_service, face_indexing_service to handle
blobs without worring of the backend.

note: prefered way to handle blob is the streamed way. Some services may not have this possibility

docs/config/env.md

@@ -8,6 +8,7 @@ Most runtime variables use the `OXICLOUD_` prefix. A few build-time or allocator
 |---|---|---|
 | `OXICLOUD_STORAGE_PATH` | `./storage` | Root storage directory |
 | `OXICLOUD_STATIC_PATH` | `./static` | Static files directory |
+| `OXICLOUD_TEMP_DIR` | `std::env::temp_dir()` (`$TMPDIR`) | Directory for tier-1 temporary data — pure scratch, safe to lose at reboot. Backend services stream blobs here when extractors need a `&Path` (id3, mp3_duration, ffprobe, nom-exif video). Files are auto-removed after use. On Linux `/tmp` is often tmpfs (RAM-backed); point at a disk-backed dir under RAM-constrained deployments. |
 | `OXICLOUD_SERVER_PORT` | `8086` | Server port |
 | `OXICLOUD_SERVER_HOST` | `127.0.0.1` | Server bind address (IPv4 or IPv6 allowed) |
 | `OXICLOUD_BASE_URL` | (auto) | Public base URL for share links; defaults to `http://{host}:{port}` |