test(realestate): add pytest harness with isolated SQLite fixture

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

realestate-lab/tests/test_db_basic.py

@@ -0,0 +1,11 @@
+def test_init_db_creates_tables():
+    from app.db import _conn
+    with _conn() as conn:
+        tables = {row[0] for row in conn.execute(
+            "SELECT name FROM sqlite_master WHERE type='table'"
+        )}
+    assert "announcements" in tables
+    assert "announcement_models" in tables
+    assert "user_profile" in tables
+    assert "match_results" in tables
+    assert "collect_log" in tables