fix(model): don't clobber local flags when receiving index (#10190)

internal/db/sqlite/sql/migrations/folder/03-drop-bad-invalid.sql

@@ -0,0 +1,17 @@
+-- Copyright (C) 2025 The Syncthing Authors.
+--
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this file,
+-- You can obtain one at https://mozilla.org/MPL/2.0/.
+
+-- Remove broken file entries in the database.
+DELETE FROM files
+    WHERE type == 0 -- files
+        AND NOT deleted -- that are not deleted
+        AND blocklist_hash IS null -- with no blocks
+        AND local_flags & {{.LocalInvalidFlags}} == 0 -- and not invalid
+;
+
+-- Force a new index transmission.
+DELETE FROM indexids
+;