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>

web_src/js/features/repo-editor.ts

@@ -1,6 +1,7 @@
 import {html, htmlRaw} from '../utils/html.ts';
-import {createCodeEditor} from './codeeditor.ts';
-import {hideElem, queryElems, showElem, createElementFromHTML} from '../utils/dom.ts';
+import {createCodeEditor} from '../modules/codeeditor/main.ts';
+import {trimTrailingWhitespaceFromView} from '../modules/codeeditor/utils.ts';
+import {hideElem, queryElems, showElem, createElementFromHTML, onInputDebounce} from '../utils/dom.ts';
 import {POST} from '../modules/fetch.ts';
 import {initDropzone} from './dropzone.ts';
 import {confirmModal} from './comp/ConfirmModal.ts';
@@ -50,8 +51,12 @@ export function initRepoEditor() {
     });
   }
 
+  // ATTENTION: two pages have this filename input
+  // * new/edit file page: there is a code editor
+  // * upload page: there is no code editor, but a uploader
   const filenameInput = document.querySelector<HTMLInputElement>('#file-name')!;
   if (!filenameInput) return;
+  filenameInput.value = filenameInput.defaultValue; // prevent browser from restoring form values on refresh
   function joinTreePath() {
     const parts = [];
     for (const el of document.querySelectorAll('.breadcrumb span.section')) {
@@ -143,7 +148,8 @@ export function initRepoEditor() {
 
   const elForm = document.querySelector<HTMLFormElement>('.repository.editor .edit.form')!;
 
-  // on the upload page, there is no editor(textarea)
+  // see the ATTENTION above, on the upload page, there is no editor(textarea)
+  // so only the filename input above is initialized, the code below (for the code editor) will be skipped
   const editArea = document.querySelector<HTMLTextAreaElement>('.page-content.repository.editor textarea#edit_area');
   if (!editArea) return;
 
@@ -170,16 +176,22 @@ export function initRepoEditor() {
 
   (async () => {
     const editor = await createCodeEditor(editArea, filenameInput);
+    filenameInput.addEventListener('input', onInputDebounce(() => editor.updateFilename(filenameInput.value)));
 
     // Update the editor from query params, if available,
     // only after the dirtyFileClass initialization
     const params = new URLSearchParams(window.location.search);
     const value = params.get('value');
     if (value) {
-      editor.setValue(value);
+      editor.view.dispatch({
+        changes: {from: 0, to: editor.view.state.doc.length, insert: value},
+      });
     }
 
     commitButton.addEventListener('click', async (e) => {
+      if (editor.trimTrailingWhitespace) {
+        trimTrailingWhitespaceFromView(editor.view);
+      }
       // A modal which asks if an empty file should be committed
       if (!editArea.value) {
         e.preventDefault();