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>

.forgejo/workflows/ci.yml

@@ -0,0 +1,15 @@
+name: build
+on: [push, pull_request]
+
+jobs:
+  build:
+    # On Codeberg's hosted runner use a label such as `codeberg-tiny`.
+    runs-on: docker
+    container:
+      image: node:22-bookworm
+    steps:
+      # Forgejo resolves actions from data.forgejo.org, hence the full URL.
+      - uses: https://data.forgejo.org/actions/checkout@v4
+      - run: npm ci
+      - run: npm run typecheck
+      - run: npm run build