gitea: default repo setting; editor: asset picker with thumbnail grid

Gitea plugin: default_repo field per account (stored in DB, pre-fills
create issue form but stays editable). Editor toolbar: asset picker
flyout with 4-column thumbnail grid and live search filter. Clicking
a tile inserts the matching markdown.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

public/plugins/tests/tests.js

@@ -50,6 +50,7 @@ const FILES = [
     './relay.test.js',
     './notifications.test.js',
     './quick-capture.test.js',
+    './asset-picker.test.js',
     './theme.test.js',
 ];