feat: add OAuth token authentication support (#236)

* feat: add OAuth token authentication support

Add claude_code_oauth_token as an alternative authentication method to anthropic_api_key.
This provides more flexibility for users who prefer OAuth authentication.

- Add claude_code_oauth_token input to action.yml
- Pass OAuth token through to claude-code-base-action
- Update README with OAuth token documentation and examples
- Update security best practices to cover both authentication methods
- Add OAuth example to examples/claude.yml

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* docs: add OAuth token generation instructions for Pro/Max users

Update README to mention that Pro and Max users can generate OAuth tokens
by running `claude setup-token` locally. This provides clearer guidance
for users who want to use OAuth authentication instead of API keys.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* docs: update CI capabilities documentation

- Move GitHub Actions access from limitations to capabilities in README
- Update FAQ to explain how to enable CI/CD access with actions:read permission
- Clarify that Claude can access workflow results on PRs where it's tagged

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>

action.yml

@@ -65,6 +65,9 @@ inputs:
   anthropic_api_key:
     description: "Anthropic API key (required for direct API, not needed for Bedrock/Vertex)"
     required: false
+  claude_code_oauth_token:
+    description: "Claude Code OAuth token (alternative to anthropic_api_key)"
+    required: false
   github_token:
     description: "GitHub token with repo and pull request permissions (optional if using GitHub App)"
     required: false
@@ -147,6 +150,7 @@ runs:
         use_bedrock: ${{ inputs.use_bedrock }}
         use_vertex: ${{ inputs.use_vertex }}
         anthropic_api_key: ${{ inputs.anthropic_api_key }}
+        claude_code_oauth_token: ${{ inputs.claude_code_oauth_token }}
         claude_env: ${{ inputs.claude_env }}
       env:
         # Model configuration