fix: drop vim mode, pin CodeMirror to dodge esm.sh outage

esm.sh's build backend was returning HTTP 500 for unbuilt @codemirror/*@6
version ranges (out of disk). A failed top-level module import aborts the
whole <script type=module>, so fillLangs()/loadModels() never ran and the
language/model dropdowns came up empty despite a healthy backend.

- Pin CodeMirror imports to already-built versions (view@6.36.0,
  state@6.7.0, commands@6.10.4), which esm.sh serves fine during the outage.
- Remove vim editing mode entirely (@replit/codemirror-vim import, vim()
  extension, Vim.mapCommand H/L bindings, .cm-vim-panel CSS). The
  document-level Shift-H/L focus cycling is retained.
- Bump to 0.4.0.

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

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "finrod"
-version = "0.3.0"
+version = "0.4.0"
 description = "Translator UI backed by Ollama"
 requires-python = ">=3.11"
 dependencies = [