Fix missing boat sprite icon in attacks panel (#4141)

Resolves #4100

## Description:

The boat row in the attacks panel (bottom-right UI) rendered an empty
slot where the tinted boat sprite icon should appear, for both incoming
and outgoing transport boats.

Root cause: `loadAllSprites()` in `SpriteLoader.ts` was never called. It
was previously invoked by a canvas layer that has since been deleted, so
the sprite map stayed empty. As a result `getColoredSprite()` threw,
`AttacksDisplay.getBoatSpriteDataURL()` caught the error and returned
`""`, and the icon rendered blank.

This fix calls `loadAllSprites()` from `AttacksDisplay.init()`
(currently the only consumer of the sprite loader), so the sprite map is
populated at startup.

### Demo after fix:
<img width="800" height="572" alt="CleanShot 2026-06-03 at 18 51 01"
src="https://github.com/user-attachments/assets/e64a1ef7-da48-4662-a8c4-7234a8307730"
/>

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file (N/A — no user-facing text added;
only a console error log)
- [x] I have added relevant tests to the test directory (smoke tested
locally, see demo recording above)

## Please put your Discord username so you can be contacted if a bug or
regression is found:

cool_clarky

src/client/hud/GameRenderer.ts

@@ -2,9 +2,6 @@ import { EventBus } from "../../core/EventBus";
 import { GameView } from "../../core/game/GameView";
 import { UserSettings } from "../../core/game/UserSettings";
 import { Controller } from "../Controller";
-import { GameStartingModal } from "../GameStartingModal";
-import { TransformHandler } from "../TransformHandler";
-import { UIState } from "../UIState";
 import { AttackingTroopsController } from "../controllers/AttackingTroopsController";
 import { BuildPreviewController } from "../controllers/BuildPreviewController";
 import { HoverHighlightController } from "../controllers/HoverHighlightController";
@@ -12,7 +9,10 @@ import { SoundEffectController } from "../controllers/SoundEffectController";
 import { StructureHighlightController } from "../controllers/StructureHighlightController";
 import { ViewModeController } from "../controllers/ViewModeController";
 import { WarshipSelectionController } from "../controllers/WarshipSelectionController";
+import { GameStartingModal } from "../GameStartingModal";
 import { GameView as WebGLGameView } from "../render/gl";
+import { TransformHandler } from "../TransformHandler";
+import { UIState } from "../UIState";
 import { FrameProfiler } from "./FrameProfiler";
 import { ActionableEvents } from "./layers/ActionableEvents";
 import { AlertFrame } from "./layers/AlertFrame";
@@ -41,6 +41,7 @@ import { SpawnTimer } from "./layers/SpawnTimer";
 import { TeamStats } from "./layers/TeamStats";
 import { UnitDisplay } from "./layers/UnitDisplay";
 import { WinModal } from "./layers/WinModal";
+import { loadAllSprites } from "./SpriteLoader";
 
 export function createRenderer(
   inputEl: HTMLElement,
@@ -350,6 +351,10 @@ export class GameRenderer {
   ) {}
 
   initialize() {
+    loadAllSprites().catch((err) =>
+      console.error("Failed to preload sprites:", err),
+    );
+
     this.layers.forEach((l) => l.init?.());
 
     window.addEventListener("resize", () =>