Fix: media worker crashes silently before writing error state

The worker called _resolve_jellyfin() and client.libraries() OUTSIDE the
try/except block. If Jellyfin was unreachable, the worker crashed with
an unhandled exception and NO error state was written to the DB — the
status stayed 'queued' forever with zero feedback.

Moved _resolve_jellyfin + client.libraries INSIDE the try block, and
created final_index + staging_index BEFORE the try so the except handler
can write the error state. Now any failure (connection refused, timeout,
missing config) is written to the DB as build_error and the frontend
shows it inline.

283 backend tests pass; ruff clean.

backend/src/media_library_viewer_api/workers/media_index_worker.py

@@ -121,9 +121,11 @@ def run_build(final_index_path: str | Path, staging_index_path: str | Path, serv
     settings = get_settings()
     configure_logging(settings.log_level)
     logger.info("Media index worker starting: %s", describe_settings(settings))
-    client, user_id = _resolve_jellyfin(service_id)
-    libraries = client.libraries(user_id)
 
+    # Create the indexes BEFORE the try block so the except handler can write
+    # error state to the DB. If _resolve_jellyfin or client.libraries fails,
+    # the worker needs to record the error — otherwise the status stays
+    # "queued" forever with no feedback.
     final_index = MediaIndex(final_index_path)
     staging_index = MediaIndex(staging_index_path)
     pid = os.getpid()
@@ -131,10 +133,13 @@ def run_build(final_index_path: str | Path, staging_index_path: str | Path, serv
 
     staging_path = Path(staging_index.db_path)
     staging_path.unlink(missing_ok=True)
-    logger.info("Media index worker pid=%s libraries=%s", pid, len(libraries))
-    _start_state(final_index, pid, len(libraries))
 
     try:
+        client, user_id = _resolve_jellyfin(service_id)
+        libraries = client.libraries(user_id)
+        logger.info("Media index worker pid=%s libraries=%s", pid, len(libraries))
+        _start_state(final_index, pid, len(libraries))
+
         count = build_media_index(
             client,
             user_id,