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>

interfaces/Crafter.Review-Pool.cppm

@@ -193,7 +193,9 @@ export namespace Crafter::Review::Pool {
 
     struct SchedulerOptions {
         Runner* runner = nullptr;
-        std::int64_t concurrency = 8;
+        // Passes in flight at once on this machine (with a board, every
+        // driver's counted); none: only each seat's own cap.
+        std::optional<std::int64_t> concurrency;
         Log log;
         std::optional<std::filesystem::path> progressPath;
         double pauseAt = 85;

interfaces/Crafter.Review-Run.cppm

@@ -46,7 +46,11 @@ export namespace Crafter::Review::Run {
         // --units, split on commas.
         std::optional<std::set<std::string>> units;
         bool warm = false;
-        std::int64_t concurrency = 128;
+        // A cap on the passes in flight on this machine, every driver's
+        // counted; none by default (2026-10-31, Jorijn: "there is no need to
+        // do a global cap anymore, the cap should be 128 per available
+        // account"): each account's own cap is the limit.
+        std::optional<std::int64_t> concurrency;
         std::string effort;
         std::int64_t reads = Plan::Reads;
         bool noReuse = false;