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

src/common/config.rs

@@ -2252,6 +2252,19 @@ pub struct AppConfig {
     pub storage_path: PathBuf,
     /// Static files directory path
     pub static_path: PathBuf,
+    /// Directory for tier-1 temporary data — pure scratch, safe to
+    /// lose at reboot. Backend `stream_to_tempfile` writes here so
+    /// extractors that require a `&Path` (id3, mp3_duration,
+    /// ffprobe, nom-exif video) can operate on a local file
+    /// without the service ever seeing a raw blob path.
+    ///
+    /// Env: `OXICLOUD_TEMP_DIR`. Default: `std::env::temp_dir()`
+    /// (respects `$TMPDIR`). On Linux this is typically `/tmp`,
+    /// often mounted as tmpfs (RAM-backed); production
+    /// deployments concerned about physical RAM under
+    /// high concurrency should point this at a disk-backed
+    /// directory (e.g. `/var/lib/oxicloud/tmp`).
+    pub temp_dir: PathBuf,
     /// Server port
     pub server_port: u16,
     /// Server host
@@ -2356,6 +2369,7 @@ impl Default for AppConfig {
         Self {
             storage_path: PathBuf::from("./storage"),
             static_path: PathBuf::from("./static"),
+            temp_dir: env::temp_dir(),
             server_port: 8086,
             server_host: "127.0.0.1".to_string(),
             cache: CacheConfig::default(),
@@ -2394,6 +2408,10 @@ impl AppConfig {
             config.static_path = PathBuf::from(static_path);
         }
 
+        if let Ok(temp_dir) = env::var("OXICLOUD_TEMP_DIR") {
+            config.temp_dir = PathBuf::from(temp_dir);
+        }
+
         if let Ok(server_port) = env::var("OXICLOUD_SERVER_PORT")
             && let Ok(port) = server_port.parse::<u16>()
         {