ci: rebuild release pipeline around OSS manifest protocol

Replace the broken yarn/Node 18 release workflow (wrong package manager,
missing build/ dir, archived actions) with a manifest-based distribution
flow modeled on yaklang/browser-binaries-mirror:

- scripts/package-release.mjs: package the four variants, emit
  release-entry.json and per-artifact sha256 checksums
- scripts/build-manifest.mjs: merge into a bounded public manifest
  (10 versions) with invariant validation
- scripts/publish-oss.mjs: immutable artifacts (forbid-overwrite,
  one-year cache) and mutable manifest (5-minute cache, checksum
  published second), idempotent via head + sha256 comparison
- scripts/verify-public.mjs: post-publish verification from the public
  endpoint (bytes, headers, zip layout)
- release.yml: pnpm + Node 22, full verify:production, OSS publish,
  GitHub Release, separate public verify job, publish concurrency group
- ci.yml: run verify:production on push/PR
- single-source the extension version in package.json (wxt.config reads)
- document the distribution protocol in README

.github/workflows/ci.yml

@@ -0,0 +1,37 @@
+name: CI
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ci-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  verify:
+    name: Test and build
+    runs-on: ubuntu-latest
+    timeout-minutes: 20
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Setup pnpm
+        uses: pnpm/action-setup@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '22'
+          cache: 'pnpm'
+
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+
+      - name: Test, compile, build and audit all variants
+        run: pnpm verify:production