fix(fc3c): explicit import of download task module in registration test

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_download_source_task.py

@@ -1,11 +1,17 @@
-"""Smoke test that the Celery task is registered and routed correctly."""
+"""Smoke test that the FC-3c Celery task is registered and routed correctly.
 
+Mirrors test_tasks_register.py — Celery's `include=[...]` is lazy, so
+the task module must be imported explicitly to trigger registration.
+"""
+
+# Side-effect import: the @celery.task decorator on download_source fires
+# at module import time and registers the task with the global instance.
+import backend.app.tasks.download  # noqa: F401
 from backend.app.celery_app import celery
 
 
 def test_download_source_is_registered():
-    name = "backend.app.tasks.download.download_source"
-    assert name in celery.tasks
+    assert "backend.app.tasks.download.download_source" in celery.tasks
 
 
 def test_download_source_routes_to_download_queue():