docs(scripts): correct frank-archon's step-sharing and slot-count comments

The env comment claimed BUSY_PREFILL_CHUNK=auto protects decode rows; the 1.8.1
source (core/sched/scheduler.cpp busy_cap) reserves 1+spec rows per decoding
sequence and 1/8 of the budget per waiting request, and refuses to shrink the
chunk for decoders alone -- auto is a prefill-speed dial. The interleave comment
carried a 512 that is not this build's auto value (0 until the held-step
counter asks; 64 in help mode). The serve header still described three decode
slots; MAX_SEQS has been 2 since the 2026-10-19 reslice. No behavior change.

scripts/serve-frank-archon.sh

@@ -15,13 +15,16 @@
 # log states every budget before anything is allocated (weights vs KV
 # split, the expert host pool's coverage of the worst case, the PLE pin,
 # the P2P answer per pair) — read it after every resize.
-# Deployed shape (2026-10-19, radiance 1.8.1): THREE decode slots x 200,000
-# tokens, fp8 KV, 44 GiB/rank pinned expert pool, MTP depth 2, prefix cache in
-# pinned host RAM, PLE pinned in RAM. The per-card split between the expert slab
-# and the KV pool is NO LONGER an operator number — 1.3.0 removed the VRAM pair
-# and the budget resolver derives it from headroom, the cache bound and the host
-# pool, so the slab size and the pool's token count are LEDGER lines: after every
-# boot read them out of the log and check the pool still backs 3 x 200,000.
+# Deployed shape (2026-10-19, radiance 1.8.1): TWO decode slots x 200,000 tokens,
+# fp8 KV, 44 GiB/rank pinned expert pool, MTP depth 2, prefix cache in pinned host
+# RAM, PLE pinned in RAM. The per-card split between the expert slab and the KV
+# pool is NO LONGER an operator number — 1.3.0 removed the VRAM pair and the budget
+# resolver derives it from headroom, the cache bound and the host pool, so the slab
+# size and the pool's token count are LEDGER lines. After every boot read them, plus
+# the two lines that size a prefill step — "activation arena: ... lends ... while
+# steps are at most N tokens" (the arena levels the expert slab borrows) and
+# "prefill staging: ... a step of more than N tokens ..." (the chunk size below which
+# pooled experts are read synchronously) — and the cache's session backing.
 #
 # The root unit (scripts/frank-archon.service, User=dank,
 # LimitMEMLOCK=infinity) grants the pin budget: 2 x 44 GiB expert pools +