Migrate from yarn to pnpm

This comprehensive migration includes:

### Configuration Updates
- Updated root package.json with pnpm workspace configuration
- Added packageManager field and pnpm overrides for graphql version
- Updated GitHub Actions workflows (.github/workflows/ci.yml, code-size.yml)
- Updated Netlify configuration (netlify.toml)
- Updated deployment script (deploy.sh)

### Documentation Updates
- Updated all README files to use pnpm instead of yarn
- Updated installation and build instructions across packages:
  - packages/webamp/README.md
  - packages/webamp-modern/README.md
  - packages/webamp-docs/README.md
  - packages/ani-cursor/README.md
  - packages/webamp/demo/readme.md

### Lock File Migration
- Removed yarn.lock
- Generated pnpm-lock.yaml preserving exact dependency versions
- Moved resolutions from skin-database package.json to root pnpm overrides
- Created pnpm-workspace.yaml for optimized workspace configuration

### CI/CD Updates
- Updated all yarn commands to use pnpm equivalents
- Changed yarn workspace commands to pnpm --filter syntax
- Updated cache keys to use pnpm-lock.yaml instead of yarn.lock
- Added pnpm/action-setup for GitHub Actions

### Validation
- Tested builds for webamp, webamp-modern, ani-cursor, webamp-docs
- Tested installation and linting for skin-database
- Verified dependency resolution consistency
- Confirmed all scripts work with pnpm

All package versions remain identical to yarn.lock, ensuring no breaking changes.

.github/workflows/code-size.yml

@@ -9,6 +9,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v2
+    - name: Install pnpm
+      uses: pnpm/action-setup@v2
+      with:
+        version: 8
     - uses: preactjs/compressed-size-action@v2
       with:
         repo-token: "${{ secrets.GITHUB_TOKEN }}"