Iteration 7: add minimal MCP debug surface

[HimanM]

Summary

• add a small MCP debug route for listing tools and making explicit kapruka_* test calls during demos
• add lightweight guardrails so only kapruka_* tools with small JSON payloads can be called from the debug surface
• document the verification and keep the previously shipped provider fallback/model defaults unchanged

Verification

• python -m unittest tests.test_mcp_debug_route tests.test_provider_selection tests.test_mcp_client tests.test_chat_route
• npm.cmd run lint
• npm.cmd run build
• live local route checks against http://127.0.0.1:8000/api/mcp/debug for successful GET and guarded invalid POST