feat: seed default plugins/pipelines, auto-enqueue jobs on asset ingest

- Migration seeds metadata_extractor, sidecar_sync, no_op plugins
- Pipelines: extract_metadata → metadata_extractor, sync_sidecar → sidecar_sync
- Worker reacts to AssetIngested → enqueues ExtractMetadata job
- Worker reacts to SidecarSyncRequested → enqueues SyncSidecar job
- Closes the ingest-to-processing loop end-to-end

crates/adapters/postgres/src/processing/mod.rs

@@ -1,4 +1,4 @@
-use crate::helpers::{pg_repo, MapDomainError};
+use crate::helpers::{MapDomainError, pg_repo};
 use async_trait::async_trait;
 use chrono::{DateTime, Utc};
 use domain::{