refactor(lifecycle hooks): simplify integration of new services

* make more coherent lifecycles
  * remove specific implementation on different handlers (they do not need to know existence of ThumbnailSerice nor AudioMetadataService)
  * reduce risk of orphean objects
  * ensure additional services are correctly wired (ex: Thumbnail generation was not covering all upload cases)
  * more details on docs/architecture/file-and-blob-lifecycle.md :

```rust
// application/ports/file_lifecycle.rs
pub trait FileLifecycleHook {

    fn on_file_created(file_id, blob_hash, content_type, is_new_blob);
    fn on_file_updated(file_id, blob_hash, content_type);
    fn on_file_copied(file_id, blob_hash, content_type, source_id)
    fn on_file_deleted(file_id);
}

// application/ports/blob_lifecycle.rs
pub trait BlobLifecycleHook {

    fn on_blob_created(blob_hash, content_type);
    fn on_blob_deleted(blob_hash);
}
```

src/application/services/blob_lifecycle_service.rs

@@ -0,0 +1,44 @@
+use std::sync::Arc;
+
+use crate::application::ports::blob_lifecycle::BlobLifecycleHook;
+
+/// Composite dispatcher for blob lifecycle events.
+///
+/// Aggregates all [`BlobLifecycleHook`] implementations and fans out each
+/// event to every registered handler. Services hold a single
+/// `Arc<BlobLifecycleService>` — new handlers are added once, in DI, without
+/// touching the services themselves.
+pub struct BlobLifecycleService {
+    hooks: Vec<Arc<dyn BlobLifecycleHook>>,
+}
+
+impl Default for BlobLifecycleService {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl BlobLifecycleService {
+    pub fn new() -> Self {
+        Self { hooks: Vec::new() }
+    }
+
+    pub fn with_hook(mut self, hook: Arc<dyn BlobLifecycleHook>) -> Self {
+        self.hooks.push(hook);
+        self
+    }
+}
+
+impl BlobLifecycleHook for BlobLifecycleService {
+    fn on_blob_created(&self, blob_hash: &str, content_type: Option<&str>) {
+        for hook in &self.hooks {
+            hook.on_blob_created(blob_hash, content_type);
+        }
+    }
+
+    fn on_blob_deleted(&self, blob_hash: &str) {
+        for hook in &self.hooks {
+            hook.on_blob_deleted(blob_hash);
+        }
+    }
+}