fix(qwen38): the rig's card split is inherited, not invented

run-qwen38-bf16.sh carried its own --host-pool-mib 12288 / --gpu-headroom-mib 768,
copied from the w4-era swift15 rig. The engine derives the whole per-card split from
those two numbers, and the KV cache's funding is `elastic - expert_floor` where the
expert floor is a function of the pinned host pool — so the pool buys cache as well
as residency. The first kldref boot got a 270 MiB / 7,436-position pool and the
recorder refused all 197 corpus documents ("document 0 is 10554 tokens and the KV
pool holds 7436"), exiting 1.

The rig now sources FRANK_ARCHON_HOST_POOL_MIB / FRANK_ARCHON_GPU_HEADROOM_MIB from
scripts/frank-archon.env, the file that owns them (49152 / 96), with `:?` guards, and
the header records the law instead of the claim that the pool never touches logits.
tests/qwen38_reference.bats pins the shape verbatim, so its SHAPE contract moves with
it; the suite is green (558 tests).

tests/qwen38_reference.bats

@@ -29,7 +29,7 @@ RUNNER="$REPO_ROOT/scripts/run-qwen38-bf16.sh"
 # The reference shape, spelled exactly as run-qwen38-bf16.sh must pass it: this
 # is the contract the recorded reference is measured at, so a silent edit here
 # is a silent edit to every KLD number in the campaign.
-SHAPE="--tp 2 --placement expert_tiered --weights-disk-tier --host-pool-mib 12288 --gpu-headroom-mib 768 --deterministic --num-speculative-tokens 0 --kv-cache-dtype fp8 --max-model-len 32768 --ngram-placement ram --override-chat-template /models/tpl.jinja"
+SHAPE="--tp 2 --placement expert_tiered --weights-disk-tier --host-pool-mib 49152 --gpu-headroom-mib 96 --deterministic --num-speculative-tokens 0 --kv-cache-dtype fp8 --max-model-len 32768 --ngram-placement ram --override-chat-template /models/tpl.jinja"
 
 # oneline — both dry runs print one shell-quoted argument a line; joining them
 # lets an option and its value be asserted as the pair they are.