fix: move ai-worker-gemma4.js to public/ — 404 on production Vite build

All other AI workers (ai-worker.js, ai-worker-docling.js, etc.) are in public/
so Vite copies them into dist/ during the production build. ai-worker-gemma4.js
was placed at the repo root — works on localhost (Vite dev serves all root files)
but returns 404 on textagent.github.io because the built dist/ doesn't include it.

Author: ijbo

changelogs/CHANGELOG-gemma4-worker-public-dir.md

@@ -0,0 +1,5 @@
+# Fix: Move ai-worker-gemma4.js to public/
+
+All other AI workers live in public/ so Vite copies them to dist/ for production.
+ai-worker-gemma4.js was mistakenly created at the repo root — works on localhost
+(Vite dev serves root files) but 404s on production GitHub Pages build.