main: GDK_SCALE is read once

Both popups read it, each just before its own textinit, and the second
copy needed a comment to say why it was there at all.  One frontend runs
per session and popupscale is one global, so threadmain reads it before it
starts either -- which is before any setfont, the only ordering the two
copies were keeping.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

main.c

@@ -47,11 +47,15 @@ erealloc(void *p, ulong n)
 void
 threadmain(int argc, char **argv)
 {
-	char *display;
+	char *display, *scale;
 
 	if(argc != 2)
 		usage();
 
+	/* Whichever popup runs is sized from it, and setfont reads Fontsz. */
+	scale = getenv("GDK_SCALE");
+	if(scale != nil && atoi(scale) > 1)
+		popupscale = min(atoi(scale), 4);
 	drawc = chancreate(sizeof(Drawcmd), 4);
 	keyc = chancreate(sizeof(Keyreq), 0);
 	langinit(argv[1]);