docs: the max-length sweep tabled; frank-small.env NGL/FLASH_ATTN restored

- runbook: identity now 4x262144, audio verified, throughput table with
  the OOM and negative-result rows, deployed flags updated to reality.
- AGENTS.md frank-small paragraph matches the deployed shape.
- log.md: the sweep entry.
- scripts/frank-small.env: my earlier line-range edit had clobbered
  NGL=999 and FLASH_ATTN=on out of the file; the seams caught it. The
  live service was unaffected because the script's defaults match the
  declared values exactly, but the file contract is restored.
Suite: ALL TESTS PASSED (321), vault 125 pages 0 unresolved.

scripts/frank-small.env

@@ -89,6 +89,11 @@ UBATCH_SIZE=1024
 # -- this host's CPU is shared with halogen's engine, which is CPU-hungry.
 NUM_THREADS=8
 THREAD_BATCH=8
+
+# Every layer on the 3090, with flash attention (required for q8 KV).
+NGL=999
+FLASH_ATTN=on
+
 # Speculative decoding: the MTP sidecar (draft context) chained with the
 # draftless ngram-mod matcher. Draft depth and busy-wait level are made
 # explicit here (both were the implicit build defaults: 3 and 50).