HUD: dpl2d Y grows down -- unflip the whole 2D layer

Period VHS footage of a 4.10 game (operator's capture) shows the twist
dial UNDER the reticle and the range bar filling top-to-bottom; our
mapping of dpl2d Y straight onto GL's Y-up NDC (and the software path's
"y up" projection) rendered the entire HUD vertically flipped.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

dpl3-revive/patha/vrview.py

@@ -1008,8 +1008,10 @@ class Renderer:
         g = 1.0 / self.gamma
 
         def P(pt):
+            # dpl2d Y grows DOWN (screen convention; period VHS footage:
+            # twist dial UNDER the reticle, range bar filling top-to-bottom)
             return (int((pt[0] - x0) * sx + 0.5),
-                    int((y1 - pt[1]) * sy + 0.5))       # y up
+                    int((pt[1] - y0) * sy + 0.5))
 
         try:
             prims = hud2d_prims(board.dl2d, root)