feat(mcp): add format argument to tool parameter schemas
Summary
- Adds an optional
formatparameter ("llm"or"raw") to bothquery_graphandget_graph_schematool JSON schemas - Enables MCP consumers to request structured JSON output instead of the default LLM-optimized text
- Cleans up tool registry: extracts test helpers, removes boilerplate
The format parameter is optional and defaults to llm (current behavior). A companion Rails MR will plumb the value through call_tool.rb to the existing format-aware gRPC layer.
Relates to #271 Relates to #433 Relates to gitlab-org#20566