feat(opensandbox): complete admin integration (#1202)

[zpzjzj]

Summary

Completes the planned OpenSandbox backend integration after #1203, #1233, and #1262.

• skip the Ray/Rocklet worker scheduler and worker /ops tasks when runtime.operator_type is opensandbox
• add a real Admin lifespan startup regression test for the OpenSandbox configuration
• add synchronized English and Chinese OpenSandbox backend guides with configuration, routing contracts, sessions, proxy behavior, and a capability matrix
• keep AOne-specific endpoint and wildcard-domain behavior out of the open-source implementation and documentation

Compatibility decisions

• OpenSandbox sandboxes do not install or require Rocklet, and ROCK does not fall back to Rocklet for this backend.
• The scheduler gate is backend-specific: existing Ray/Kubernetes behavior is preserved.
• HTTP and WebSocket service proxying use the generic endpoint-discovery contract returned by OpenSandbox; ROCK does not assume a path-routing or wildcard-domain deployment strategy.
• Unsupported operations remain explicit: stop/restart persistence, interactive session commands, archive/restore/image commit, and raw TCP forwarding are not added here.

Validation

• uv run ruff check and uv run ruff format --check on all changed Python files
• 296 targeted scheduler/OpenSandbox/Admin tests passed
• real FastAPI Admin lifespan startup passed with OpenSandbox selected and scheduler enabled, while asserting Ray and worker scheduler initialization are skipped
• both new MDX guides compiled independently
• CI-equivalent Docusaurus production build passed for English and zh-Hans with Node 20 and webpack 5.105.4; only pre-existing scheduler anchor warnings remain

Delivery plan

This is the final planned OpenSandbox integration PR. After this PR, only review or CI fixes will be folded into this same branch; no additional feature PR is currently planned for issue #1202.

The 1.11 documentation version registration is already handled by #1300. Until #1300 lands, these versioned guide files compile but are not linked by the published version selector.

Closes #1202