feat(topology): add Flask app skeleton with db connection (psycopg 3)

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

topology_api/db.py

@@ -0,0 +1,34 @@
+# topology_api/db.py
+import psycopg
+from psycopg.rows import dict_row
+from contextlib import contextmanager
+from topology_api.config import READER_DATABASE_URL, WRITER_DATABASE_URL
+
+
+def get_reader_connection():
+    """Return a new read-only connection with dict_row rows."""
+    return psycopg.connect(READER_DATABASE_URL, row_factory=dict_row)
+
+
+def get_writer_connection():
+    """Return a new write-capable connection with dict_row rows."""
+    return psycopg.connect(WRITER_DATABASE_URL, row_factory=dict_row)
+
+
+@contextmanager
+def read_cursor():
+    """Context manager for read queries. Returns a cursor."""
+    with get_reader_connection() as conn:
+        conn.execute("SET search_path TO topology, public")
+        with conn.cursor() as cur:
+            yield cur
+
+
+@contextmanager
+def write_cursor():
+    """Context manager for write queries. Auto-commits on success, rollback on error."""
+    with get_writer_connection() as conn:
+        conn.execute("SET search_path TO topology, public")
+        with conn.transaction():
+            with conn.cursor() as cur:
+                yield cur