fix: update CI workflows from yarn to npm, add CNAME for GitHub Pages

- publish.yml: yarn → npm ci/npm run build, add cname option
- checks.yml: yarn → npm ci/npm run, pin actions/checkout@v4
- cd-manual.yml: yarn → npm ci/npm run, remove corepack

The production site (simpleserialize.com) is deployed via Cloudflare
Pages using cd-manual.yml (manual dispatch). The GitHub Pages deploy
goes to chainsafe.github.io/simpleserialize.com/.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: wemeetagain

.github/workflows/cd-manual.yml

@@ -9,16 +9,12 @@ jobs:
       contents: read
       deployments: write
     steps:
-      - uses: actions/checkout@v5
-      - run: corepack enable
-      - uses: actions/setup-node@v5
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
         with:
-          cache: yarn
           node-version: "22"
-      - name: Bootstrap
-        run: yarn --immutable
-      - name: Build
-        run: yarn build
+      - run: npm ci
+      - run: npm run build
       - name: Publish to Cloudflare Pages
         uses: cloudflare/pages-action@1
         with:

.github/workflows/checks.yml

@@ -6,8 +6,12 @@ jobs:
   Checks:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
-      - run: yarn install
-      - run: yarn build
-      - run: yarn check-types
-      - run: yarn lint
+      - uses: actions/checkout@v4
+      - name: Setup Node
+        uses: actions/setup-node@v4
+        with:
+          node-version: "22"
+      - run: npm ci
+      - run: npm run build
+      - run: npm run check-types
+      - run: npm run lint

.github/workflows/publish.yml

@@ -14,11 +14,12 @@ jobs:
         uses: actions/setup-node@v4
         with:
           node-version: "22"
-      - run: yarn
-      - run: yarn build
+      - run: npm ci
+      - run: npm run build
       - name: Deploy
         uses: peaceiris/actions-gh-pages@v3
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_branch: gh-pages
           publish_dir: ./dist
+          cname: simpleserialize.com