feat: status notes when every gated cap is at the bar but aggregate headroom remains

## What

When every account's gated per-model cap is at the bar, the pool is depleted for that model even though weekly aggregate headroom remains for other models. Nothing surfaces this. The owner sees depleted waits; the usable headroom is invisible.

## Evidence

Live pool, 2026-09-13: 13 of 16 accounts at Fable weekly 98 to 100 with weekly aggregates at 59 to 92. 63 all-depleted decisions in 46 hours of log.

## Why this is wrong

The aggregate headroom is spendable by non-gated models. An operator who cannot see it cannot act on it, and the depleted path gives no hint that the constraint is per-model rather than total quota.

## Fix direction

In `status` (text and `--json`, through the collect step per the output contract): when every account that carries a gated window has it at or over the weekly bar, and at least one account's weekly aggregate is under the bar, print a note naming the capped family and the number of accounts with aggregate headroom.

## Related

#81