Remove unused Structure Sprites setting

The structureSprites toggle was only read by the toggle UIs themselves —
no rendering code ever consulted it. Drops the getter/setter from
UserSettings, both toggle rows (SettingsModal + UserSettingModal), and
the en.json keys. Other-language entries are left for Crowdin to reap.

src/client/UserSettingModal.ts

@@ -230,15 +230,6 @@ export class UserSettingModal extends BaseModal {
     );
   }
 
-  private toggleStructureSprites() {
-    this.userSettings.toggleStructureSprites();
-
-    console.log(
-      "🏠 Structure sprites:",
-      this.userSettings.structureSprites() ? "ON" : "OFF",
-    );
-  }
-
   private toggleCursorCostLabel() {
     this.userSettings.toggleCursorCostLabel();
 
@@ -787,15 +778,6 @@ export class UserSettingModal extends BaseModal {
         @change=${this.toggleFxLayer}
       ></setting-toggle>
 
-      <!-- 🏠 Structure Sprites -->
-      <setting-toggle
-        label="${translateText("user_setting.structure_sprites_label")}"
-        description="${translateText("user_setting.structure_sprites_desc")}"
-        id="structure_sprites-toggle"
-        .checked=${this.userSettings.structureSprites()}
-        @change=${this.toggleStructureSprites}
-      ></setting-toggle>
-
       <!-- 💰 Cursor Price Pill -->
       <setting-toggle
         label="${translateText("user_setting.cursor_cost_label_label")}"