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/runner.js

@@ -180,6 +180,7 @@ export async function closeAll() {
     document.querySelector('.bucket-picker')?.remove();
     document.querySelector('.orphan-lightbox')?.remove();
     document.getElementById('bucket-super-popover')?.remove();
+    document.getElementById('asset-picker-flyout')?.remove();
     document.getElementById('gitea-overlay')?.classList.remove('open');
     // Clear multi-select
     document.querySelectorAll('.card-selected').forEach(el => {