Probe Wise

Prove the pasted Wise key actually works, on demand -- WisePanel.tsx calls this right after a save, the same "save then verify" shape /api/system/wise/probe exists to give a person immediate feedback for, rather than waiting on the next /api/health poll's cached result (wise.PROBE_CACHE_TTL_SECONDS).

No generic POST /credentials/{name}/probe route exists yet (nothing else needed one), so this is Wise's own, gated exactly like every other System write. Never raises on a bad key -- wise.probe_wise_key is itself non-raising and records the verdict either way; this only translates that into what the panel shows.