feat(studio): add frontend-owned client tools

[evanlowe]

Summary

• add a versioned per-run client tool protocol so Studio can provide missing tools while native Runtime tools keep precedence
• add read-only Janus browser context and Studio-hosted presentation, image, and video fallbacks with availability and tool-span feedback
• scope traces to the selected assistant turn, remove the private Node PPT dependency, render content-based previews, and contain wide message output

Testing

• cd frontend && npm test (439 passed)
• cd frontend && npm run build
• uv run pytest tests/cli/test_frontend_apmplus_trace.py tests/cli/test_studio_rbac.py tests/cli/test_frontend_client_tools.py tests/integrations/agentkit/test_session_capabilities.py tests/tools/test_ppt_generate.py (72 passed)
• pre-commit run --all-files
• cloud smoke test for browser context and turn-scoped traces