feat: integrate OIDC token exchange in GitHub Action

- Add setupGitHubInstallationToken utility for OIDC token generation
- Implement automatic token exchange with Pullfrog API endpoint
- Add support for multiple authentication methods (input, env, OIDC)
- Create setup utilities for test repository management
- Update action entry point to handle new token flow
- Add environment variable documentation for API key
- Remove large bundled dependencies and optimize build
- Support both development and production token workflows

README.md

@@ -55,6 +55,14 @@ pnpm dev          # Watch mode
 
 The action is bundled into `entry.cjs` with all dependencies included, eliminating runtime dependency on node_modules.
 
+## Environment Variables
+
+Create `.env` in `/action`:
+
+```bash
+ANTHROPIC_API_KEY=sk-ant-api03-xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx  # Claude API key
+```
+
 ## Architecture
 
 - **entry.cjs**: Bundled action entry point (self-contained)