frank-primary: util 0.90 — production bf16 boot OOM fix

The 0.98 boot died at KV allocation: torch OOM tried 10.28 GiB (the exact
3x262144 bf16 pool = 11,047,010,304 bytes) with 9.46 GiB free per rank.
The rootless bench probe had booted the same numbers; the root unit's
pinned-expert path holds ~0.8 GiB/rank more. Util 0.90 returns ~2.5 GiB/rank
of workspace with the pool ask unchanged; measured KV capacity law
(798,280 tokens at 11.05e9) unchanged.

scripts/frank-primary.env

@@ -67,4 +67,4 @@ FRANK_PRIMARY_KV_DTYPE=auto
 FRANK_PRIMARY_MNBT=1024
 FRANK_PRIMARY_GATHER_CHUNKS=32
 FRANK_PRIMARY_GATHER_LANES=64
-FRANK_PRIMARY_UTIL=0.98
+FRANK_PRIMARY_UTIL=0.90