feat: host coverage card and ak run records #368

Why

Every host and every supervised run is counted (design: Every host).

In scope

Record each ak run worker in the cache (host, folder, start and end, outcome, model when known), with schema room for execution identity and configured-versus-observed model (G10, EV E1); detect Hermes, Gemini CLI and other known hosts without reading their history; the coverage card.

Out of scope

Reading unsupported hosts (v5).

Acceptance criteria

• An unread host shows as a gap, never a zero
• ak run records appear in Activity

Dependencies

Blocked by: #364

Blocks: #257, #370, #387, #255, #239, #407, #413

Plan

• Release: 4.0.0-beta.3
• Size: size:M · Workstream: ws:project-scope
• Epic: feat: project-scope P6, the dashboard for all work (epic) #301
• Card: P6-05 in the card inventory
• Sources: Design (docs(plans): project-scoped management design and its prerequisites #289) Every host; Supersession ledger (docs(plans): v4 GA master plan, supersession ledger and v5 registers #290) G10

Verification

• node scripts/run-tests.mjs focus (new coverage tests)