refactor(onitama): centralize visual constants in config

Introduce `TEXT_POSITION` and `VISUAL` objects to the configuration
to manage magic numbers for positioning, radii, stroke widths, and
alphas. Update renderers and spawners to use these constants instead
of hardcoded values or direct calculations.

packages/onitama-game/src/scenes/OnitamaScene.ts

@@ -10,6 +10,8 @@ import {
   COLORS,
   FONTS,
   MENU_BUTTON,
+  TEXT_POSITION,
+  VISUAL,
   getBoardCenter,
   getCardLabelPosition,
   colorToStr,
@@ -79,7 +81,12 @@ export class OnitamaScene extends GameHostScene<OnitamaState> {
     });
 
     // Info text
-    this.infoText = this.add.text(40, BOARD_OFFSET.y, "", FONTS.info);
+    this.infoText = this.add.text(
+      TEXT_POSITION.infoX,
+      BOARD_OFFSET.y,
+      "",
+      FONTS.info,
+    );
 
     // Update info text when UI state changes
     this.addEffect(() => {
@@ -149,7 +156,12 @@ export class OnitamaScene extends GameHostScene<OnitamaState> {
 
     g.strokePath();
 
-    this.add.text(40, 40, "Onitama", FONTS.title);
+    this.add.text(
+      TEXT_POSITION.titleX,
+      TEXT_POSITION.titleY,
+      "Onitama",
+      FONTS.title,
+    );
   }
 
   private setupInput(): void {
@@ -288,7 +300,7 @@ export class OnitamaScene extends GameHostScene<OnitamaState> {
         boardWidth,
         boardHeight,
         COLORS.overlayBg,
-        0.6,
+        VISUAL.overlayAlpha,
       )
       .setInteractive({ useHandCursor: true });