Pin the keyword models to one thread each and ship them (V-487)

The gate loaded and worked on workpc and took mavwaked from 68% of one core
to 335%. onnxruntime sizes its intra-op pool to every core and spins between
runs, which an always-on gate scoring three graphs twelve times a second
provokes for the whole day. One thread per session brings it to 81%, so the
keyword costs about 13% of a core, and each graph still finishes well inside
its 80ms.

The unit now passes the three -wake- flags and the models sit beside
silero_vad.onnx in ~/.local/share/maven/models. The threshold is left at the
binary's default so there is one place to change it.

docs/evals/2026-08-09-wake-word.md

@@ -94,6 +94,14 @@ the head the whole request to peak during. A bare "Мэйвен" with nothing af
 it is the case that fails. One fix would hold an ignored utterance for a grace
 period and ship it if the keyword lands late. It is not built.
 
+## What it costs the workstation
+
+Under systemd on workpc, mavwaked sat at 335% of a core with the gate on and
+68% with only silero. onnxruntime sizes its thread pool to every core and spins
+between runs, and this gate runs three graphs twelve times a second. Pinning
+all three sessions to one thread brought it to 81%, so the keyword costs about
+13% of one core. The three graphs each finish in well under 80ms that way.
+
 ## What was not measured
 
 No room recordings. Every negative above is a clean corpus clip. This gate