Record the smoke-validated numbers behind MAIN_BOX_UNITS

The smoke run confirmed the width model against the real engine: room width
20 units, ~0.137 units/char at scale 0.32, and the geometry path clamps
correctly. That pins the no-clip margin -- subtracting 4.6 for a ~3.1-3.3
unit desc box keeps the budget under true capacity at every card position,
including one right at the 40% flip. Note it in the comment so it reads as
validated, not a guess. No behaviour change.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

main.lua

@@ -626,8 +626,10 @@ JCA._wrap_text = wrap_text
 local ROW_BUDGET_MIN = 24
 local ROW_BUDGET_MAX = 60
 -- The card's OWN description popup sits between our tooltip and the card, eating
--- into the gutter. Approximate in game units; dbg() logs the inputs so it can be
--- tuned against a real hover.
+-- into the gutter. A joker's desc box is ~3.1-3.3 units wide; we subtract 4.6 so
+-- the budget always UNDER-estimates the true capacity -- with the smoke-measured
+-- metric (roomw 20, ~0.137 units/char at scale 0.32) that margin keeps every
+-- card, even one right at the 40% flip, clear of the edge. dbg() logs the inputs.
 local MAIN_BOX_UNITS = 4.6
 
 -- Width of one average character in room units at a text scale, from the game's