feat: list repository commits

[aeitwoen]

Summary

• add paginated commit summaries to the provider API and every agent surface
• map ref, path, since, and until filters across GitHub, GitLab, and Gitea
• reject Gitea path filtering explicitly because its API ignores pagination limits
• keep changed-file details in the existing single-commit operation

Testing

• pnpm lint
• pnpm typecheck
• pnpm vitest run --maxWorkers=8
• pnpm test:packed
• anonymous live reads against GitHub, GitLab, and Gitea

Closes #63