feat(console): support multiple worker systems per user

[Coooolfan]

Summary

• Allow one account to own multiple worker-sys workers; removes the worker_sys_owner_claims single-per-account constraint and the 409 conflict on create.
• Breaking: computerUse now dispatches only when worker_id selects a caller-owned Worker System (pinned, no fallback); without worker_id the task completes locally and returns worker_list of all owned Worker Systems.
• readImage / exportFile target a Worker System via session_id="CU:<worker_id>"; other values keep sandbox session semantics. Prefix is configurable via computer_use_session_id_prefix / CONSOLE_COMPUTER_USE_SESSION_ID_PREFIX (default CU:), and terminalExec rejects create_if_missing on reserved-prefix session IDs.
• Migration 00009 drops the claims table; rollback is rejected while any account owns multiple worker-sys workers.
• Updated docs/API*.md, website docs (EN/zh-CN), and added 0.12.0-beta.1 release notes.

Test plan

• task_worker_sys_routing_test.go: computerUse list mode / worker_id routing, readImage prefix routing, reserved-prefix rejection
• db_test.go / migration tests: rollback guard with multiple worker-sys per owner
• command_handler_test.go, mcp_handler_test.go, connect_service_test.go, integration_test.go updated for new semantics

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.