Replaces the Task 1 stub. Builds an EditorView with:
- history, line numbers, active-line highlight, bracket matching,
close brackets, indent-on-input
- default + custom HighlightStyle
- light/dark theme via matchMedia-driven Compartment with a
prefers-color-scheme change listener
- language via Compartment (swappable for the files-modal dropdown)
- autocomplete via Compartment (only if vocab is provided)
- keymap stack: closeBrackets, default, history, completion, indentWithTab
Mounts the EditorView immediately before the textarea, hides the
textarea. Exposes window.__editor.mount(textarea, opts) returning a
controller with getValue / setContent / setLanguage / destroy.
bash language comes via @codemirror/legacy-modes/mode/shell wrapped
in StreamLanguage.define — same mechanism as srccfg.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
