Draft: feat: implement get_repository_file MCP tool
Relates to issue #566140
Changes
- Add get_repository_file MCP tool to Repository Files API endpoint
- Map to existing GET /projects/:id/repository/files/:file_path endpoint
- Support required parameters: id, file_path, ref
- Follow established MCP framework pattern using route_setting annotation
- Add Duo Context Exclusion support using Ai::FileExclusionService