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>

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

examples/claude.yml

@@ -33,4 +33,6 @@ jobs:
         uses: anthropics/claude-code-action@beta
         with:
           anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
+          # Or use OAuth token instead:
+          # claude_code_oauth_token: ${{ secrets.CLAUDE_CODE_OAUTH_TOKEN }}
           timeout_minutes: "60"