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>

package.json

@@ -0,0 +1,21 @@
+{
+  "name": "diff-highlighter",
+  "version": "1.0.0",
+  "description": "Chrome extension that highlights .diff and .patch files — additions green, deletions red, with toggleable syntax highlighting.",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "typecheck": "tsc --noEmit",
+    "build": "tsc --noEmit && node scripts/build.mjs",
+    "watch": "node scripts/build.mjs --watch"
+  },
+  "dependencies": {
+    "highlight.js": "^11.10.0"
+  },
+  "devDependencies": {
+    "@types/chrome": "^0.0.287",
+    "@types/node": "^22.10.0",
+    "esbuild": "^0.28.1",
+    "typescript": "^5.7.2"
+  }
+}