feat: vendor all browser deps into the image (no runtime CDN)

esm.sh's degraded storage backend served an unpinned transitive
@codemirror/view@^6.27.0 range URL as text/plain, which browsers block for
a disallowed MIME type. A failed top-level module import aborts the whole
<script type=module>, so the language/model dropdowns came up empty despite
a healthy backend — and top-level version pinning can't fix a transitive
range.

Add a frontend/ esbuild stage (Node stage in the Dockerfile) that vendors
everything into static/vendor and serve only from there:
- CodeMirror (view/state/commands) bundled into one self-contained ESM file
- cropperjs (+ CSS) copied from npm dist
- Tesseract.js engine + wasm core + Dutch (nld) language pack; OCR assets
  stay lazy (fetched only when a scan runs) and fully local
- Drop vim mode (@replit/codemirror-vim); keep document-level Shift-H/L

Google Fonts remains the only external <link> (degrades gracefully, not in
the failing path). Bump to 0.5.0.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitignore

@@ -7,3 +7,7 @@ __pycache__/
 .mypy_cache/
 .idea/
 .vscode/
+
+# Frontend vendor bundle is produced at Docker build time (frontend/build.mjs).
+node_modules/
+static/vendor/