feat(sdk): end-user health surface widget over the control plane [SD-6]

[rickylabs]

Part of #830 (gap G8 — the POC's "silently broken features" fix). SDK client/widget over the control plane (in-process link #451 or loopback), per-user read tokens; "service X restarting…" surfaced in the app UI.

Depends on: #832, #451.

• gate: contract-client conformance; full frontend overlay (loading/error/responsive/browser); jsr rubric on the SDK surface

Design source: PR #822 (rfc.md + plan.md rev 10, 9-cycle adversarial trail) in .llm/runs/rfc-single-deployment--orchestrator/.