feat: DEFAULT_TOPICS_SEED + ensure_topics_seeded

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

tests/e2e.py

@@ -278,6 +278,27 @@ def t_topics_helpers():
     assert get_topics() == sample2
 
 
+def t_topics_seeded_after_assign():
+    from app import get_topics, _empty_state, save_data, load_data
+    # 빈 상태로 reset
+    save_data(_empty_state())
+    assert get_topics() == []
+
+    from assign_teams import ensure_topics_seeded
+    data = load_data()
+    ensure_topics_seeded(data)
+    save_data(data)
+
+    cats = get_topics()
+    assert len(cats) == 4
+    for c in cats:
+        assert len(c["items"]) == 10
+        assert c["id"] in ("T1", "T2", "T3", "T4")
+        assert c["title"]
+        assert c["tagline"]
+        assert c["tone"]
+
+
 if __name__ == "__main__":
     print(f"# E2E (data={TEST_DATA})\n")
     test("hackathon.json 로드 (34명, 7팀)", t_load)
@@ -296,6 +317,7 @@ if __name__ == "__main__":
     test("load_data nested 키 backfill", t_load_data_backfills_nested_settings)
     test("stage 헬퍼", t_stage_helpers)
     test("topics 헬퍼", t_topics_helpers)
+    test("topics 시드", t_topics_seeded_after_assign)
 
     fails = sum(1 for r, _ in results if r == FAIL)
     print(f"\n# {len(results)} 중 통과 {len(results) - fails}, 실패 {fails}")