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>

CHANGELOG.md

@@ -7,6 +7,14 @@ Versioning: [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
 
+## [0.4.0] - 2026-07-05
+
+### Removed
+- Vim editing mode. Dropped the `@replit/codemirror-vim` import and its `Vim.mapCommand` H/L focus bindings. The document-level Shift-H/L focus cycling across the dropdowns/buttons is retained (it never depended on vim). One fewer esm.sh dependency.
+
+### Fixed
+- Empty language and model dropdowns when esm.sh cannot serve an unpinned `@codemirror/*@6` range (their build backend was returning HTTP 500 on unbuilt versions). A failed top-level module import aborts the whole `<script type="module">`, so `fillLangs()`/`loadModels()` never ran despite a healthy backend. CodeMirror imports are now pinned to already-built versions (`view@6.36.0`, `state@6.7.0`, `commands@6.10.4`).
+
 ## [0.3.0] - 2026-06-09
 
 ### Added