fix(gemini): remove unsupported propertyNames schemas

[christophertjiattas]

Summary

• remove the JSON Schema propertyNames keyword while building Gemini function declarations
• preserve the existing recursive sanitization behavior for nested object schemas
• add a regression test covering nested free-form map parameters, such as Playwright MCP tool data

Gemini rejects propertyNames in function-declaration parameters with HTTP 400 (Unknown name "propertyNames").

Testing

• uv run pytest tests/test_gemini_model_full_coverage.py
• uv run pytest -q
• uv run ruff check .
• uv run ruff format --check .