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_gl.py

@@ -196,6 +196,10 @@ in vec2 in_pos;
 void main() {
     vec2 p = vec2((in_pos.x - u_rect.x) / (u_rect.z - u_rect.x),
                   (in_pos.y - u_rect.y) / (u_rect.w - u_rect.y)) * 2.0 - 1.0;
+    // dpl2d Y grows DOWN (screen convention): period VHS footage shows the
+    // twist dial UNDER the reticle and the range bar filling top-to-bottom;
+    // mapping straight onto GL's Y-up NDC rendered the whole HUD flipped.
+    p.y = -p.y;
     gl_Position = vec4(p, 0.0, 1.0);
 }
 """