Initial commit: Diff Highlighter Chrome extension (MV3, TypeScript)

Highlights .diff/.patch files inline — additions green, deletions red,
hunk/file headers styled, with toggleable highlight.js syntax highlighting.

- MV3, content script gated on text/plain + URL ending in .diff/.patch
- Two-phase render: instant diff colors, then chunked idle-time syntax
- Popup switches + Alt+D shortcut, persisted in chrome.storage.sync, live re-render
- Light/dark via prefers-color-scheme; only the `storage` permission
- TypeScript + esbuild build; Forgejo Actions CI (typecheck + build)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

scripts/build.mjs

@@ -0,0 +1,57 @@
+// Builds the extension into dist/: bundles the TypeScript entry points with
+// esbuild and copies the static assets (manifest, popup HTML, CSS, icons).
+// Run `node scripts/build.mjs` for a one-shot build, or with `--watch` for dev.
+import * as esbuild from 'esbuild';
+import { cp, mkdir, rm } from 'node:fs/promises';
+import { existsSync } from 'node:fs';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const root = path.resolve(path.dirname(fileURLToPath(import.meta.url)), '..');
+const dist = path.join(root, 'dist');
+const watch = process.argv.includes('--watch');
+
+/** Copy a file or directory from a repo-relative path into dist/ (flattened). */
+async function copy(from, to) {
+  const src = path.join(root, from);
+  if (!existsSync(src)) return;
+  await cp(src, path.join(dist, to), { recursive: true });
+}
+
+async function copyStatic() {
+  await copy('src/manifest.json', 'manifest.json');
+  await copy('src/popup/popup.html', 'popup.html');
+  await copy('src/styles/diff.css', 'diff.css');
+  await copy('src/styles/hljs-theme.css', 'hljs-theme.css');
+  await copy('src/styles/popup.css', 'popup.css');
+  await copy('icons', 'icons');
+}
+
+const options = {
+  entryPoints: {
+    content: path.join(root, 'src/content.ts'),
+    background: path.join(root, 'src/background.ts'),
+    popup: path.join(root, 'src/popup/popup.ts'),
+  },
+  outdir: dist,
+  entryNames: '[name]',
+  bundle: true,
+  format: 'iife',
+  target: ['chrome120'],
+  minify: !watch,
+  sourcemap: watch ? 'inline' : false,
+  logLevel: 'info',
+};
+
+await rm(dist, { recursive: true, force: true });
+await mkdir(dist, { recursive: true });
+await copyStatic();
+
+if (watch) {
+  const ctx = await esbuild.context(options);
+  await ctx.watch();
+  console.log('watching for changes…');
+} else {
+  await esbuild.build(options);
+  console.log('built ->', path.relative(root, dist));
+}