Validate merged comment-ops config against a JSON Schema

[Copilot]

The app loaded .github/comment-ops.yml and merged it with defaults, but never verified that the resulting config matched the supported shape. This adds runtime schema validation using a validator that supports the current JSON Schema spec and rejects malformed command config early.

• Schema validation

  • add a JSON Schema 2020-12 definition for the supported commands structure
  • validate booleans for toggle-only commands and string arrays for allowedLabels
  • reject unknown properties within command blocks to keep config shape explicit

• Router integration

  • validate the merged config returned by octokit.config.get(...) before command execution
  • keep validation at the existing config boundary so org/repo/default merging is checked as one final object

• Focused coverage

  • add tests for:
    • default config
    • valid label config with allowedLabels
    • invalid boolean types
    • invalid allowedLabels types
    • unexpected extra properties

• Example

  const { config } = await octokit.config.get({
    owner,
    repo,
    path: ".github/comment-ops.yml",
    defaults: (configs) => deepmerge.all([defaultConfig, ...configs]),
  });
  
  validateConfig(config);

• Fixes Validate config schema #61