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.

dankclaw/voiceservice/quadlet/frank-tts.container

@@ -37,8 +37,9 @@
 # has a second backend (`TTS_BACKEND=llama-tts-cli`) that needs no upstream, and
 # an engine that will not start must not take this endpoint's unit down with it.
 # When both boot, this comes up after the engine, whose ExecStartPost warm pass
-# is part of its start — so the first request of the day meets a warm voice
-# registry instead of paying the 5.5 s cold decode.
+# is part of its start — so the first request of the day meets a REGISTERED voice
+# (the registry is memory-only) rather than a 400, and skips the ~0.6 s penalty
+# the first synthesis of an unwarmed voice costs.
 #
 # VOICES. /home/dank/voices is host state, never repo state, and is mounted
 # READ-ONLY: this endpoint has no business writing voice packs. Because the