feat(studio): add versioned Codex sandbox environments

[evanlowe]

Summary

• refine Studio environment creation and support preset AIO Sandbox and Codex Sandbox environments
• add versioned v3 environment APIs while preserving existing v2 Studio clients and reconciling v2/v3 storage
• create and reuse one Sandbox Tool session per mounted environment and Agent session
• route mounted Codex Sandbox tasks through the App Server and render status, reasoning, commands, results, usage, and final responses
• deduplicate final answers and enforce UTF-8-safe tool-result limits
• restore long session-title hover/focus scrolling and rebuild packaged WebUI assets

Validation

• uv run pytest tests/frontend/server/environments tests/frontend/server/studio_tools tests/cli/test_frontend_invocation.py tests/cli/test_frontend_runtime_proxy.py tests/integrations/agentkit/test_studio_channel.py (294 passed)
• cd frontend && npm test (995 passed)
• cd frontend && npm run build
• cd frontend && npm run test:webui-assets (96 packaged files and 240 internal references)
• pre-commit run
• desktop visual review at 1200x887
• mobile visual review at 390x844 with no horizontal overflow

Notes

• Python Pyright reports existing baseline diagnostics in legacy modules; none intersects the lines added by this change.