Add triage bundle endpoint for one-call system diagnosis

[spinchange]

Problem

Agents currently need multiple calls to form a first-pass system diagnosis.

Proposal

Add get_umi_triage_bundle as a one-call triage entrypoint.

Acceptance Criteria

• New get_umi_triage_bundle endpoint exists.
• Returns summary, top processes, top grouped events, service health, and highlights.
• Default payload is compact enough for normal LLM use.
• In common cases, an agent can answer what is wrong right now from this call alone.