feat(realestate-db): add district / notify / 5tier columns with migration

- announcements.district + idx_ann_district 인덱스
- user_profile: preferred_districts(JSON obj), min_match_score(int 70), notify_enabled(bool)
- match_results: notified_at(TEXT)
- _profile_row_to_dict: notify_enabled bool화, preferred_districts dict 역직렬화
- PROFILE_COLUMNS 확장 (3 신규 필드)
- upsert_profile: list|dict 모두 JSON 직렬화

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

realestate-lab/tests/test_db_migration.py

@@ -0,0 +1,39 @@
+def test_user_profile_has_new_columns():
+    from app.db import _conn
+    with _conn() as conn:
+        cols = {row["name"] for row in conn.execute("PRAGMA table_info(user_profile)")}
+    assert "preferred_districts" in cols
+    assert "min_match_score" in cols
+    assert "notify_enabled" in cols
+
+
+def test_announcements_has_district():
+    from app.db import _conn
+    with _conn() as conn:
+        cols = {row["name"] for row in conn.execute("PRAGMA table_info(announcements)")}
+    assert "district" in cols
+
+
+def test_match_results_has_notified_at():
+    from app.db import _conn
+    with _conn() as conn:
+        cols = {row["name"] for row in conn.execute("PRAGMA table_info(match_results)")}
+    assert "notified_at" in cols
+
+
+def test_district_index_exists():
+    from app.db import _conn
+    with _conn() as conn:
+        idx = {row["name"] for row in conn.execute(
+            "SELECT name FROM sqlite_master WHERE type='index'"
+        )}
+    assert "idx_ann_district" in idx
+
+
+def test_profile_defaults():
+    from app.db import upsert_profile, get_profile
+    upsert_profile({"name": "테스트"})
+    profile = get_profile()
+    assert profile["preferred_districts"] == {}
+    assert profile["min_match_score"] == 70
+    assert profile["notify_enabled"] is True