fix(ci): add Bun setup and build steps to npm publish workflow

The npm publish was failing because:
1. Bun runtime was not installed (prepublishOnly uses bun commands)
2. dist/ was not built before publish

Added:
- oven-sh/setup-bun@v2 action
- bun install step
- bun run build step

.github/workflows/publish-npm.yml

@@ -22,6 +22,17 @@ jobs:
           node-version: '20'
           registry-url: 'https://registry.npmjs.org'
 
+      - name: Setup Bun
+        uses: oven-sh/setup-bun@v2
+        with:
+          bun-version: latest
+
+      - name: Install dependencies
+        run: bun install
+
+      - name: Build package
+        run: bun run build
+
       - name: Sync version from VERSION file
         run: node scripts/sync-version.js