docs(frank-tts): retire the 5.5 s cold-voice claim everywhere it still lived

PR #15 corrected the engine's page, the research brief's law bullet and the
warmer's header, but the retired ladder had six more homes: both quadlet files
("6.2-8.0 s… 0.5 ms", "~6-8 s each", "paying the 5.5 s cold decode"),
`scripts/frank-tts-engine.env` (the whole law paragraph and the WARM_TEXT note),
`scripts/frank-tts.env`, the [[Frank TTS]] troubleshooting row that told an
operator to expect ~5.5 s, the research brief's consequences paragraph, and one
test comment.

All re-keyed to what was measured on the deployed container 2026-10-18: the
first synthesis of a freshly registered voice costs 1,883 ms against 1,226-1,283
ms afterwards, so the warm pass buys about 0.6 s — and the reason it exists at
all, which the pages never led with, is that the registry is memory-only: without
the hook every voice name is a 400 until somebody synthesizes. The trial's dated
worklog entry stays as written; the correction points at it.

No behavior change: comments, unit lore and docs only, so no cfhash move and no
image rebuild.

scripts/frank-tts.env

@@ -35,8 +35,9 @@
 #                  shim resolves the voice and re-encodes to mp3 when asked. The
 #                  shipped engine (frank-tts-engine) speaks a voice it has
 #                  REGISTERED on itself, from the same /home/dank/voices packs,
-#                  and warms them at boot — see [[Frank TTS Engine]] for why an
-#                  unwarmed voice costs the first caller 5.5 s.
+#                  and warms them at boot — see [[Frank TTS Engine]] for what that
+#                  boot warm is for (a memory-only registry: without it every name
+#                  is a 400) and what it saves (~0.6 s).
 #   llama-tts-cli  run LLAMA_TTS_BIN once per request with
 #                  --tts-speaker-file <reference.wav>, nice 19 so a narration
 #                  never starves the text endpoints on this box. Needs