Home's builders tile says why builders are idle: the ceiling, no ready issue, or no subscription with headroom #5799

Part of #5735. The cold read missed why the builders sat idle.

Done when:

• [ ] When builders running is below the slots, the builders tile (and its line in kpiLines) names the first reason that holds, in this order: ceiling reached, no subscription with headroom, nothing ready. Each reason links to the page that fixes it: /meter, /subscriptions, the map.
• [ ] The reason comes from the same checks the crew's scheduler uses before it starts a run. Do not re-derive the rule.
• [ ] One test per reason seeds that state and finds the words on / and in the terminal dashboard.
• [ ] When every slot is busy, no reason is shown.

Files: src/flow/kpis.ts, src/flow/kpi_words.ts, src/web/studio/kpi_row.ts, src/tui/screens/dashboard.ts, tests. Risk: this touches the same tile files as the ceiling issue. Keep the change to the builders tile.

Parked by the crew: the check stayed red through 2 automatic tries (pull #5819 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.

Parked by the crew: the check failed ("budgets > /map and / answer under their p95 and statement budgets") and the decider saw no point in another try try 1: src/crew/idle.ts, src/flow/kpi_words.ts, src/flow/kpis.ts, src/tui/screens/dashboard.ts (+4 more) try 2: AGENTS.md, CLAUDE.md, README.md, charts/app/templates/deployment.yaml (+1002 more) (pull #7008 closed).

Parked twice since a person last spoke here, so it is the planner's now. Every reason:

1. the check stayed red through 2 automatic tries (pull #5819 closed)
2. the check failed ("budgets > /map and / answer under their p95 and statement budgets") and the decider saw no point in another try try 1: src/crew/idle.ts, src/flow/kpi_words.ts, src/flow/kpis.ts, src/tui/screens/dashboard.ts (+4 more) try 2: AGENTS.md, CLAUDE.md, README.md, charts/app/templates/deployment.yaml (+1002 more) (pull #7008 closed)

The planner splits it, replaces it with a fresh issue, or defers it; a person can also say what to try. Nothing starts here until then, and the board lists it.

Planner: split into #7663, #7664 and #7665. Both tries put the rule, the home tile and the terminal into one pull. Computing the reason on every home load broke the home's statement budget ("budgets > /map and / answer under their p95 and statement budgets"). Try 2's branch also carried more than 1,000 unrelated files.

The new pieces:

• #7663 is the rule alone, reusing the dispatcher's own checks, now including flow only.
• #7664 is the home tile, read inside the cached KPI answer, so it waits for #7624.
• #7665 is the terminal dashboard.