docs(sightsound): correct unknown-model-tag contract to live-probed behavior

Prior docs claimed unknown tags silently serve llama3.2:1b. Live probes on the
live endpoint disprove it: /v1/chat/completions answers HTTP 200 with a flat
{"error":"Failed to load <tag> model!"} body and no choices; /v1/completions
answers a nested OpenAI-shaped server_error (code 500) under HTTP 200. Valid
tags route per-request to the named model (response echoes the requested tag);
no restart needed to switch between registry tags. Corrected in the runbook,
the AGENTS.md runtime section, the serve-script header comment, and the
historical FastFlowLM incident note.

AGENTS.md

@@ -288,8 +288,10 @@ The third inference endpoint on Dankclaw. The `flm serve` runtime (dpkg
 package `fastflowlm`, v1.0.1, binary `/usr/bin/flm`) serves the **whole local
 model registry** (36 tags at first deploy) on a single port — 52626 — and
 routes chat completions per request by the exact FLM registry tag in the
-`model` field. Unknown tags do NOT 404: they silently serve `llama3.2:1b`,
-so clients must send exact registry tags, never service aliases. Primary
+`model` field. Unknown tags do NOT 404: `/v1/chat/completions` answers HTTP 200
+with `{"error":"Failed to load <tag> model!"}` and no choices (status-only
+clients silently get nothing), so clients must send exact registry tags, never
+service aliases. Primary
 model = Gemma4 E4B IT NPU2 pack (vision + audio towers); the uncensored
 candidate (`qwythos:9b`) is text-only and fails the modality requirement, so
 this endpoint trades "uncensored" for "sight + sound". The NPU is a