Build 2602261605: invite trace and cross-system user lifecycle

backend/app/db.py

@@ -732,6 +732,42 @@ def set_user_blocked(username: str, blocked: bool) -> None:
         )
 
 
+def delete_user_by_username(username: str) -> bool:
+    with _connect() as conn:
+        cursor = conn.execute(
+            """
+            DELETE FROM users WHERE username = ? COLLATE NOCASE
+            """,
+            (username,),
+        )
+    return cursor.rowcount > 0
+
+
+def delete_user_activity_by_username(username: str) -> int:
+    with _connect() as conn:
+        cursor = conn.execute(
+            """
+            DELETE FROM user_activity WHERE username = ? COLLATE NOCASE
+            """,
+            (username,),
+        )
+    return cursor.rowcount
+
+
+def disable_signup_invites_by_creator(username: str) -> int:
+    timestamp = datetime.now(timezone.utc).isoformat()
+    with _connect() as conn:
+        cursor = conn.execute(
+            """
+            UPDATE signup_invites
+            SET enabled = 0, updated_at = ?
+            WHERE created_by = ? COLLATE NOCASE AND enabled != 0
+            """,
+            (timestamp, username),
+        )
+    return cursor.rowcount
+
+
 def set_user_role(username: str, role: str) -> None:
     with _connect() as conn:
         conn.execute(