fix: add API job poller to process scheduler-created metadata jobs

The scheduler (indexer) created metadata_refresh/metadata_batch jobs in DB,
but the indexer excluded them (API_ONLY_JOB_TYPES) and the API only processed
jobs created via its REST endpoints. Scheduler-created jobs stayed pending forever.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/api/src/metadata_batch.rs

@@ -115,14 +115,14 @@ pub async fn start_batch(
 
     let job_id = Uuid::new_v4();
     sqlx::query(
-        "INSERT INTO index_jobs (id, library_id, type, status) VALUES ($1, $2, 'metadata_batch', 'pending')",
+        "INSERT INTO index_jobs (id, library_id, type, status, started_at) VALUES ($1, $2, 'metadata_batch', 'running', NOW())",
     )
     .bind(job_id)
     .bind(library_id)
     .execute(&state.pool)
     .await?;
 
-    // Spawn the background processing task
+    // Spawn the background processing task (status already 'running' to avoid poller race)
     let pool = state.pool.clone();
     let library_name: Option<String> = sqlx::query_scalar("SELECT name FROM libraries WHERE id = $1")
         .bind(library_id)
@@ -313,7 +313,7 @@ pub async fn get_batch_results(
 // Background processing
 // ---------------------------------------------------------------------------
 
-async fn process_metadata_batch(
+pub(crate) async fn process_metadata_batch(
     pool: &PgPool,
     job_id: Uuid,
     library_id: Uuid,