feat(editor): broaden language detection in web code editor (#37619)

Use
https://github.com/github-linguist/linguist/blob/main/lib/linguist/languages.yml
to substantially improve syntax higlighting in Codemirror. File is
generated on-demand only.

Signed-off-by: silverwind <me@silverwind.io>
Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>

web_src/js/modules/codeeditor/main.test.ts

@@ -0,0 +1,54 @@
+import {buildLanguageDescriptions, importCodemirror} from './main.ts';
+
+test('matchFilename — language detection covers extended rules', async () => {
+  const cm = await importCodemirror();
+  const list = buildLanguageDescriptions(cm);
+  const match = (filename: string) =>
+    cm.language.LanguageDescription.matchFilename(list, filename)?.name;
+
+  // Linguist-supplied filenames + extensions
+  expect(match('.bashrc')).toBe('Shell');
+  expect(match('PKGBUILD')).toBe('Shell');
+  expect(match('foo.zsh')).toBe('Shell');
+  expect(match('Cargo.lock')).toBe('TOML');
+  expect(match('Gemfile')).toBe('Ruby');
+  expect(match('foo.gemspec')).toBe('Ruby');
+  expect(match('foo.psgi')).toBe('Perl');
+  expect(match('foo.pyi')).toBe('Python');
+  expect(match('foo.webmanifest')).toBe('JSON');
+  expect(match('foo.tcc')).toBe('C++');
+
+  // Script-side extras (extraFilenames / extraExtensions)
+  expect(match('.editorconfig')).toBe('Properties files');
+  expect(match('foo.conf')).toBe('Properties files');
+  expect(match('Snakefile')).toBe('Python');
+
+  // Custom Gitea entries override language-data
+  expect(match('Containerfile.test')).toBe('Dockerfile');
+  expect(match('Dockerfile.dev')).toBe('Dockerfile');
+  expect(match('Makefile.am')).toBe('Makefile');
+  expect(match('foo.mk')).toBe('Makefile');
+  expect(match('.env.local')).toBe('Dotenv');
+  expect(match('foo.json5')).toBe('JSON5');
+  expect(match('foo.mdown')).toBe('Markdown');
+
+  // Filename regex wins over extension match
+  expect(match('nginx.conf')).toBe('Nginx');
+
+  // .spec routes to RPM Spec via excludeExt redirect
+  expect(match('foo.spec')).toBe('RPM Spec');
+
+  // CM original ownership preserved against Linguist's broader claims (.sql is SQL,
+  // not PLSQL, even though Linguist's PLSQL extension list includes it).
+  expect(match('foo.sql')).toBe('SQL');
+  expect(match('foo.h')).toBe('C');
+  expect(match('foo.mm')).toBe('Objective-C++');
+
+  // Globally ambiguous extensions fall through to plain text
+  expect(match('foo.cgi')).toBeUndefined();
+  expect(match('foo.inc')).toBeUndefined();
+
+  // Smoke: existing language-data entries still resolve
+  expect(match('foo.go')).toBe('Go');
+  expect(match('foo.tsx')).toBe('TSX');
+});