Pin the producer-lead change; record what the bench measured

Bump the grblHAL pin to the producer lead and margin instrumentation.

Rewrite BRINGUP item 16 to the present state. The scheduling half is
done - the producer runs SCHED_FIFO below the shipper, core_mx carries
priority inheritance, and clamping is reported per run - and two bench
runs 90 s apart on one image show what that does and does not cover: a
nice-5 CPU hog passes clean while the camera streaming clamps 7 runs,
because per-frame cache maintenance over a 4.8 MB non-coherent capture
buffer is kernel-context work no userspace priority can preempt.

Record the margin finding, since it explains why a 4 ms stall was
enough: the queue depth cancels between the shipper's due index and the
producer's base, so the pacing lead is the only slack. Record the
cycle-churn ceiling that caps that lead at 10 ms, and that the re-base
fix is what unlocks more.

Camera gating stays owed, with capture resolution named as the lever
that shortens the stall rather than merely spacing stalls out.

meta-forgefirm/recipes-forgefirm/grblhal-glowforge/grblhal-glowforge-pin.inc

@@ -2,5 +2,5 @@
 # changes; keep only SRCREV and PV here - the image manifest leaves
 # *-pin.inc out of the layer content hash because the component entry
 # already identifies the pinned source (forgefirm-image-manifest.bbclass).
-SRCREV = "026c169c6ee028907a0235d4e3bbf5cf9d91e2a8"
+SRCREV = "fd059b3bf52de103f598cf94cb860916e5fffd00"
 PV = "0.1.0"