fix(frank-archon): fold the pinned host pool back to 49,152; keep the 2,048 step

PR #81's pool half measured inert the day it deployed: the 66,560 boot printed the
same elastic 26.73 GiB / experts 20.72 / kv cache 5.64 / vram_weights 24.30 as the
49,152 boot and opened the pool with 0 B used, and the qwen38-w5nl64 rig moved
vram_kv 269.99 -> 271.25 MiB (window still 7,436 tokens: its 95.37 GiB n-gram table
claim decides, not the pool). The step half stays. Tests: 576 ok / 0 fail.

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=66560$' "$ENV_FILE"
+    grep -q '^FRANK_ARCHON_HOST_POOL_MIB=49152$' "$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