Replace Monaco with CodeMirror (#36764)

- Replace monaco-editor with CodeMirror 6
- Add `--color-syntax-*` CSS variables for all syntax token types,
shared by CodeMirror, Chroma and EasyMDE
- Consolidate chroma CSS into a single theme-independent file
(`modules/chroma.css`)
- Syntax colors in the code editor now match the code view and
light/dark themes
- Code editor is now 12px instead of 14px font size to match code view
and GitHub
- Use a global style for kbd elements
- When editing existing files, focus will be on codemirror instead of
filename input.
- Keyboard shortcuts are roughtly the same as VSCode
- Add a "Find" button, useful for mobile
- Add context menu similar to Monaco
- Add a command palette (Ctrl/Cmd+Shift+P or F1) or via button
- Add clickable URLs via Ctrl/Cmd+click
- Add e2e test for the code editor
- Remove `window.codeEditors` global
- The main missing Monaco features are hover types and semantic rename
but these were not fully working because monaco operated only on single
files and only for JS/TS/HTML/CSS/JSON.

| | Monaco (main) | CodeMirror (cm) | Delta |
|---|---|---|---|
| **Build time** | 7.8s | 5.3s | **-32%** |
| **JS output** | 25 MB | 14 MB | **-44%** |
| **CSS output** | 1.2 MB | 1012 KB | **-17%** |
| **Total (no maps)** | 23.3 MB | 12.1 MB | **-48%** |

Fixes: #36311
Fixes: #14776
Fixes: #12171

<img width="1333" height="555" alt="image"
src="https://github.com/user-attachments/assets/f0fe3a28-1ed9-4f22-bf25-2b161501d7ce"
/>

---------

Signed-off-by: silverwind <me@silverwind.io>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Giteabot <teabot@gitea.io>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

package.json

@@ -10,12 +10,28 @@
     "@citation-js/plugin-bibtex": "0.7.21",
     "@citation-js/plugin-csl": "0.7.22",
     "@citation-js/plugin-software-formats": "0.6.2",
+    "@codemirror/autocomplete": "6.20.1",
+    "@codemirror/commands": "6.10.3",
+    "@codemirror/lang-json": "6.0.2",
+    "@codemirror/lang-markdown": "6.5.0",
+    "@codemirror/language": "6.12.3",
+    "@codemirror/language-data": "6.5.2",
+    "@codemirror/legacy-modes": "6.5.2",
+    "@codemirror/lint": "6.9.5",
+    "@codemirror/search": "6.6.0",
+    "@codemirror/state": "6.6.0",
+    "@codemirror/view": "6.40.0",
     "@github/markdown-toolbar-element": "2.2.3",
     "@github/paste-markdown": "1.5.3",
     "@github/text-expander-element": "2.9.4",
+    "@lezer/highlight": "1.2.3",
     "@mcaptcha/vanilla-glue": "0.1.0-alpha-3",
     "@mermaid-js/layout-elk": "0.2.1",
     "@primer/octicons": "19.23.1",
+    "@replit/codemirror-indentation-markers": "6.5.3",
+    "@replit/codemirror-lang-nix": "6.0.1",
+    "@replit/codemirror-lang-svelte": "6.0.0",
+    "@replit/codemirror-vscode-keymap": "6.0.2",
     "@resvg/resvg-wasm": "2.6.2",
     "@silverwind/vue3-calendar-heatmap": "2.1.1",
     "@vitejs/plugin-vue": "6.0.5",
@@ -25,6 +41,7 @@
     "chartjs-adapter-dayjs-4": "1.0.4",
     "chartjs-plugin-zoom": "2.2.0",
     "clippie": "4.1.10",
+    "codemirror-lang-elixir": "4.0.1",
     "colord": "2.9.3",
     "compare-versions": "6.1.1",
     "cropperjs": "1.6.2",
@@ -38,7 +55,6 @@
     "js-yaml": "4.1.1",
     "katex": "0.16.43",
     "mermaid": "11.13.0",
-    "monaco-editor": "0.55.1",
     "online-3d-viewer": "0.18.0",
     "pdfobject": "2.3.1",
     "perfect-debounce": "2.1.0",