feat(03-03): wire get_current_user into /api/topics/*; add load_topics_for_user; POST /api/admin/topics
- api/topics.py: add get_current_user dep to all 5 handlers (list, create, update, delete, suggest)
- list_topics: uses load_topics_for_user (system topics + user's own) with user-scoped doc counts
- create_topic: passes user_id=current_user.id (never creates system topics via regular endpoint)
- update_topic/delete_topic: ownership assertion — system topics and other users' topics return 404
- api/admin.py: add SystemTopicCreate model + POST /api/admin/topics (user_id=NULL, admin-only)
- services/storage.py: add or_ import; load_topics_for_user (D-17); create_topic gains user_id param with namespace-scoped dedup; topic_doc_counts gains optional user_id for user-scoped counts; add load_topics_for_user to __all__
- services/classifier.py: replace load_topics with load_topics_for_user(doc.user_id); pass user_id=doc.user_id to create_topic for AI-suggested topics (D-11)
- Tests: update all topic tests to pass auth headers; implement test_topic_namespace, test_admin_create_system_topic, test_regular_user_cannot_create_system_topic, test_topics_require_auth
curo1305
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