feat(frank-archon): raise the pinned host pool; the campaign inherits the step

frank-archon.env: HOST_POOL_MIB 49,152 -> 66,560 a rank (tp x 65 GiB against the
246 GiB the box has), and the TTM pair 162,000/204,800 -> 197,000/224,000 — the
floor the bats ledger formula computes at the new pool. The pool is the KV lever
under the budget resolver: every MiB pinned in host RAM lowers the expert floor on
the card one-for-one and the cache takes it.

scripts/run-qwen38-bf16.sh: the campaign's private FRANK_QWEN38_MNBT (1,024) is
gone — MNBT now comes from FRANK_ARCHON_MAX_BATCHED_TOKENS, production's 2,048 and
the widest step the quantised expert file tiers stream. That 1,024 was PR #80's
answer to a starved cache; the pool is the fix, a narrow step was the symptom's
disguise, and a per-mode literal measures a shape nothing serves.

tests: frank_archon_unit greps the new pool value; qwen38_reference's SHAPE fixture
carries it, and the two MNBT-override tests become the inheritance assertion (every
mode's argv quotes the value the env file owns) plus the calib assertions.

vault: the shape block moves to the new numbers and the Eras table gains the row for
the era this replaces. The 2026-10-20 boot-ledger line stays as the old era's record
until the new boot's ledger replaces it.

tests/frank_archon_unit.bats

@@ -158,7 +158,7 @@ nosudo_bin() {
     # so the pool's token count is a boot-ledger line — verified live by the
     # capacity leg of scripts/probe-frank-archon-kv.py at every cutover.
     grep -q '^FRANK_ARCHON_PLACEMENT=expert_tiered$' "$ENV_FILE"
-    grep -q '^FRANK_ARCHON_HOST_POOL_MIB=49152$' "$ENV_FILE"
+    grep -q '^FRANK_ARCHON_HOST_POOL_MIB=66560$' "$ENV_FILE"
     grep -q '^FRANK_ARCHON_KV_DTYPE=fp8$' "$ENV_FILE"
     grep -q '^FRANK_ARCHON_NGRAM_PLACEMENT=ram$' "$ENV_FILE"
     # Prefix cache: pinned host RAM only (the disk tier was removed), and the