feat(pool): no machine-wide width - 128 passes per available account

Jorijn: "there is no need to do a global cap anymore, the cap should be
128 per available account". `--concurrency` no longer defaults to 128:
the limits are each OAuth account's 128 (and the local login's), every
driver's counted, an API seat's own REVIEW_GATES_API_CONCURRENCY, and
free memory. `--concurrency N` still caps the machine when given; a value
below 1 is a usage error.

The dump's args.concurrency is null then. The board's driver settings
read `128 per account`, which every driver's `seats` shows as that
driver's width, and the `seats` header says a width is that driver's cap.
The Scheduler test runs 300 passes on two accounts: 256 at once, 128 each.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

AGENTS.md

@@ -110,6 +110,7 @@ Conventions:
 - **Seat placement** (SeatPool, Seats, Drivers):
   - An account whose 5-hour limit Anthropic has removed reports the weekly window alone. Its burst window (`Seats::BurstWindow`) is the weekly one: it is ranked and admitted by the weekly window with the passes in flight projected on it (0.04 points per pass at xhigh, 0.125 otherwise), under the 95 % cutoff.
   - Every OAuth account and the local login takes at most 128 passes at once, every driver's counted.
+  - There is no machine-wide width (2026-10-31, Jorijn: "there is no need to do a global cap anymore, the cap should be 128 per available account"). `--concurrency` caps only when given, and the dump's `args.concurrency` is then null. The board's driver settings read `128 per account`, which every driver's `seats` shows as that driver's width (Scheduler, Runs).
   - A 'concurrents' rejection pauses the seat for 20 s or its retry-after, not until a window's reset.
   - Board entries and the folded `foreign` record carry `cost7d`, and so does the dump's seat summary.
   - The `seats` report and the log table say `no limit` in such an account's 5-hour column.