feat: directory scanner plugin — walk library paths, auto-register assets

- DirectoryScannerPlugin: recursive directory walk via FileStoragePort
- Computes SHA256 checksums, classifies media by extension
- Registers each file via RegisterAssetHandler (triggers AssetIngested → extract_metadata pipeline)
- Reads library_path_id from job payload, looks up volume + path
- Seeded plugin + scan_directory pipeline
- Trigger via POST /jobs with { job_type: "ScanDirectory", payload: { library_path_id: "..." } }

crates/worker/src/factories/plugins.rs

@@ -1,8 +1,12 @@
 use crate::plugin_registry::InMemoryPluginRegistry;
 use crate::plugins::{
-    MetadataExtractorPlugin, NoOpPlugin, SidecarSyncPlugin, ThumbnailGeneratorPlugin,
+    DirectoryScannerPlugin, MetadataExtractorPlugin, NoOpPlugin, SidecarSyncPlugin,
+    ThumbnailGeneratorPlugin,
+};
+use application::catalog::RegisterAssetHandler;
+use domain::ports::{
+    EventPublisher, MetadataExtractorPort, SidecarWriterPort, ThumbnailGeneratorPort,
 };
-use domain::ports::{MetadataExtractorPort, SidecarWriterPort, ThumbnailGeneratorPort};
 use std::sync::Arc;
 
 use super::Repos;
@@ -13,6 +17,7 @@ pub fn build_plugin_registry(
     sidecar_writer: Arc<dyn SidecarWriterPort>,
     extractor: Arc<dyn MetadataExtractorPort>,
     thumbnail_gen: Arc<dyn ThumbnailGeneratorPort>,
+    event_pub: Arc<dyn EventPublisher>,
 ) -> InMemoryPluginRegistry {
     let mut registry = InMemoryPluginRegistry::new();
 
@@ -25,11 +30,23 @@ pub fn build_plugin_registry(
     )));
     registry.register(Arc::new(ThumbnailGeneratorPlugin::new(
         repos.asset.clone(),
-        file_storage,
+        file_storage.clone(),
         repos.derivative.clone(),
         thumbnail_gen,
     )));
 
+    let register_handler = Arc::new(RegisterAssetHandler::new(
+        repos.asset.clone(),
+        repos.duplicate.clone(),
+        event_pub,
+    ));
+    registry.register(Arc::new(DirectoryScannerPlugin::new(
+        repos.volume.clone(),
+        repos.library_path.clone(),
+        file_storage.clone(),
+        register_handler,
+    )));
+
     let export_handler = Arc::new(application::sidecar::ExportSidecarHandler::new(
         repos.metadata.clone(),
         repos.sidecar.clone(),