Admin quota adjustment now takes the per-user advisory lock and a FOR UPDATE
row lock on the quota account before projecting the balance, so the check
covers both used and reserved amounts and stays transactionally consistent
with task freeze and settlement. Settlement and lease-recovery paths also
lock the quota row explicitly.
Add the isolated Phase 5 exception-matrix harness (fault injection against a
dedicated DB + fake upstream) covering last-quota contention, concurrent
admin reduce, freeze/reduce stress, bad/oversized/timeout upstream, storage
failure, cross-period settlement and queued/running restart recovery.
Add test-only deps, provisioning helper (secrets via env) and test README.
