Make attack ring size tunable and increase it to 30px

The transport-target ring size was hardcoded as RING_SCREEN_PX in
attack-ring.vert.glsl. Promote it to a uRingScreenPx uniform fed from
a new fx.attackRingScreenPx entry in render-settings.json, with an
"Attack Ring Size (px)" slider in the debug GUI's FX folder.

Also bump the size from 20 to 30 screen px so the ring is easier
to spot. The inner/outer ring fractions (0.5/0.8 of the quad) stay
shader constants.

src/client/render/gl/debug/Layout.ts

@@ -332,6 +332,15 @@ export function buildTree(s: RenderSettings, d: RenderSettings): DebugNode[] {
 
     folder("FX", [
       slider(s.fx, "shockwaveRingWidth", d.fx, 0.01, 0.2, 0.005),
+      slider(
+        s.fx,
+        "attackRingScreenPx",
+        d.fx,
+        5,
+        60,
+        1,
+        "Attack Ring Size (px)",
+      ),
       slider(
         s.fx,
         "nukeShockwaveDurationMs",