fix(plugins): validate and surface MCP runtime lifecycle

[GTC2333]

Summary

Stage 2 PR 7/9.

• validate MCP-backed plugin activation and report startup failures
• track observed MCP server states in the runtime
• expose MCP status through the runtime/backend APIs
• show restart requirements and ready/degraded/failed states in Marketplace
• refresh composer MCP mentions after a runtime restart
• harden the bundled Playwright MCP launcher

Workspace-file-link scoping from the original development sequence is intentionally excluded; it belongs to PR 9.

Verification

• root typecheck
• 165 targeted runtime/backend tests
• 61 targeted Web tests
• Web production build
• diff whitespace validation

Merge notes

Targets main directly and does not depend on PR 5 or PR 9.

[Fxde42]

Request changes：static runtime 模式下，StaticRuntimeOrchestrator.stopRuntime 是 no-op，但 POST /runtime/restart 仍返回成功，Marketplace 随后关闭提示并把 mentions 当作已刷新，实际 runtime 和 MCP tools 都没有重启。建议 static 模式返回明确的 409 和手动重启容器指引，并保留待重启提示；不要向 UI 报告假成功。请补 StaticRuntimeOrchestrator 路径的 API 测试。

[GTC2333]

Addressed the static-runtime restart issue in c6803b3. The Orchestrator interface now exposes externally managed lifecycle ownership; /api/runtime/restart returns 409 with manual container/process restart guidance before stopping, clearing clients, or reporting success. The existing Marketplace error path retains the restart prompt and does not emit the restarted event. Added a real StaticRuntimeOrchestrator endpoint regression test. Validation: root typecheck, 117 backend/runtime tests, 62 Web tests, and Web production build.