Fix WorldTextPass labels scaling with device-pixel-ratio

Attack troop labels, the ghost-cost chip, and the bonusPopup
minScreenScale floor were dividing by `zoom`, which Camera.ts stores
as device-pixels-per-world-unit (canvasW = cssWidth * dpr). The result
was constant device-pixel size — labels rendered ~2x larger on DPR=1
displays than on retina. Multiply each screen-relative scale by dpr so
the on-screen size stays constant in CSS pixels.

Retune the now-correct sizes: attack labels 34 -> 17, ghost-cost
screenScale 30 -> 18, screenYOffset 50 -> 25.

src/client/render/gl/render-settings.json

@@ -270,8 +270,8 @@
     "cullZoom": 0.3
   },
   "ghostCost": {
-    "screenScale": 30,
-    "screenYOffset": 50
+    "screenScale": 18,
+    "screenYOffset": 25
   },
   "spawnOverlay": {
     "highlightRadius": 9,