pod: BT_GLASS=1 is not a gate -- name the real one (BT_PLATFORM=glass)

BT_GLASS is a compile-time #ifdef; getenv("BT_GLASS") appears nowhere in the
tree.  The line rode along from the bring-up launcher into the frozen profile
and into the pod-hardware runbook, reading like the switch that turns the
glass path on.  It never did anything -- the rig worked because glass is the
DEFAULT profile when nothing is set.

Replaced with BT_PLATFORM=glass (the real spelling, so the cart does not lean
on that default) and noted why NOT BT_PLATFORM=pod: the pod profile selects
the 1995 multi-surface gauge path, which needs the NVIDIA horizontal span no
modern driver has.  Behaviourally identical -- both land gBTPlatformGlass=1.

Re-verified on the cart: 9 settings applied, GLASS profile, -fit borderless,
all three surfaces on their intended displays.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Rw7No5wLTpkaUgA3ANbtZZ

scratchpad/pod/podprofile.ini

@@ -10,7 +10,14 @@
 #      VGA Port A        = monitor:DISPLAY2  (RGB triple: Heat + Comm + Mfd2)
 #      VGA Port B        = monitor:DISPLAY1  (RGB triple: Mfd1 + Mfd3)
 
-BT_GLASS=1
+# Platform PROFILE.  NB "glass", not "pod": BT_PLATFORM=pod selects the 1995
+# multi-surface gauge path (exclusive-fullscreen D3D per adapter + the NVIDIA
+# horizontal span), which no modern driver can do.  What lights this cab is the
+# GLASS profile plus the three switches below.  (Glass is already the default
+# when nothing is set -- named here so the rig never depends on that default.)
+BT_PLATFORM=glass
+
+# One window per surface -- this is the switch that makes panels at all.
 BT_GLASS_PANELS=1
 
 # ONE VGA port's R/G/B lines drive THREE mono MFDs -- composite the planes.