Decisions serving for qwen27 (Ornith-1.5-122B): score/decide passes, JointHead scoring, a free decision slot, GPU class profiling #1190

PRs in this series

Kept up to date as each pull request is opened. The whole family stacks on #1125 (the qwen27 Metal family); every branch carries its parents' commits until they merge — review only each PR's own commits, named in its body.

• qwen27: score and decide passes queued onto the lane host's idle engine thread #1189 score and decide passes queued onto the lane host's idle engine thread
• qwen27: a JointHead side-head scores options on post-norm hidden rows at their final-token positions #1191 JointHead side-head scores options on post-norm hidden rows at their final-token positions
• lanes: a queued decision takes a free slot beside the live streams, as a new stream's prompt pass would #1192 a queued decision takes a free lane slot beside the live streams
• TF_Q27_PROFILE logs the round's class GPU times; replies carry gpu_seconds (in rework)

The qwen27 Metal lane takes decision work beside text generation: an HTTP thread enqueues a score or decide task and the lane host's own engine thread runs the pass — first only at idle points (#1189), then beside live traffic on a free slot (#1192). One resident model serves both streams; there is no scheduler beside the engine.

#1191 adds a small trained side head (--joint-head) that scores each option on the post-final-norm hidden row at its own final-token position instead of label logits. The last member wires the existing gpu_profile.Trace per-class timers up on the 27B backend behind TF_Q27_PROFILE, off by default.