feat: read commit details and changed files

[oritwoen]

Summary

This lets agents inspect exact paths changed after a SHA is known without falling back to platform-specific API calls or streaming patches.

• add normalized commit metadata and changed-file rows for GitHub, GitLab, and Gitea
• expose forges_commits_get through MCP, Pi, and OMP with bounded pagination and no patches
• report count availability and file-list completeness, document the API, and cover provider and packed-extension paths

Testing

• pnpm lint
• pnpm typecheck
• pnpm test:packed
• pnpm test:run
• anonymous live commit reads against GitHub, GitLab, and Gitea

Closes #64