fix(studio): restore BytePlus Skill Hub flows

[richarddancin]

Summary

• restore the Skill Hub tab in BytePlus Studio and route creation-time Skill Hub search through the same /harness/skills/findskill endpoint used by chat
• keep BytePlus evaluation-set UI/API behavior disabled or neutral when AgentKit evaluation sets are unsupported
• repair BytePlus Studio update env handling for sandbox tool IDs and rebuild bundled web assets

Tests

• npm test -- markdownPromptEditor.test.mjs
• UV_CACHE_DIR=/tmp/uv-cache PYTHONPYCACHEPREFIX=/tmp/veadk-pycache uv run pytest tests/cli/test_frontend_evaluation_feedback.py::test_studio_findskill_route_uses_session_skillhub_search tests/cli/test_frontend_evaluation_feedback.py::test_feedback_cases_byteplus_404_reports_unsupported tests/cli/test_studio_update.py::test_byteplus_studio_update_repairs_missing_sandbox_tools -q
• npm run build
• UV_CACHE_DIR=/tmp/uv-cache PYTHONPYCACHEPREFIX=/tmp/veadk-pycache uv run pre-commit run --all-files