fix(mcp): tighten ingest traces schema for strict clients

[SyntaxSawdust]

Summary

• Declare supported ingest_traces item fields in the generated MCP schema.
• Set traces.items.additionalProperties to false for strict clients such as Visual Studio Copilot.
• Add a parsed tools/list regression test covering the nested schema path.

Why

Fixes #731.

Visual Studio Copilot rejects codebase_memory_ingest_traces because the nested trace item object schema does not explicitly set additionalProperties: false. The schema now closes that object while still advertising the existing trace payload shape: caller, callee, and optional count.

Tests

• build/c/test-runner mcp - passed, 122 tests.
• git diff --check - passed.
• make -f Makefile.cbm test - built and ran, but failed outside the MCP path with local listener/offline clone environment failures.
• make -f Makefile.cbm lint-ci - blocked locally because cppcheck is not installed.

Scope

• No runtime trace ingestion behavior changes.
• No tool names or handler dispatch changes.
• No manual Visual Studio smoke test was performed.