Support Freebuff & Codebuff

### Area

gitnexus (CLI / core / indexing / MCP server)

### Problem or opportunity

Need to support freebuff/codebuff

### Proposed solution

similar integration to other CLI

### Alternatives considered

_No response_

### Acceptance criteria

_No response_

### Constraints

_No response_

### Contribution

- [ ] I am willing to open a PR for this (may need design discussion first).