Create PublicScratchpadTool using pointer_tool.rs as a template, using scratchpad_service.rs instead of 
pointer_service.rs.

Given pointer_tool.rs reflects pointer_controller.rs, ensure PublicScratchpadTool reflects public_scratchad_controller.rs too.

Ensure all public_scratchpad_controller.rs endpoints are recreated as MCP tools (#[tool]).

Provide unit test coverage for the new tool.