feat(audio): swap to repair music while a mission is in repair flow

Switch background music to musique-reparation.mp3 whenever any mission
(ebike / pylon / farm) is in the repair mini-game step range
(inspected → done) and back to musique-jeu.mp3 once the mission
leaves that range. Reuses AudioManager.playMusic which handles the
swap cleanly when the path changes.

src/world/GameMusic.tsx

@@ -1,14 +1,43 @@
 import { useEffect } from "react";
 import { AudioManager } from "@/managers/AudioManager";
+import { useGameStore } from "@/managers/stores/useGameStore";
+import type { MissionStep } from "@/types/gameplay/repairMission";
 
 const GAME_MUSIC_PATH = "/sounds/musique/musique-jeu.mp3";
-const GAME_MUSIC_VOLUME = 0.33;
+const REPAIR_MUSIC_PATH = "/sounds/musique/musique-reparation.mp3";
+const MUSIC_VOLUME = 0.33;
+
+// Steps during which the repair mini-game owns the experience.
+// Triggered when any mission (ebike / pylon / farm) is in this range.
+const REPAIR_MUSIC_STEPS: ReadonlySet<MissionStep> = new Set([
+  "inspected",
+  "fragmented",
+  "scanning",
+  "repairing",
+  "reassembling",
+  "done",
+]);
 
 export function GameMusic(): null {
+  const ebikeStep = useGameStore((state) => state.ebike.currentStep);
+  const pylonStep = useGameStore((state) => state.pylon.currentStep);
+  const farmStep = useGameStore((state) => state.farm.currentStep);
+
+  const inRepair =
+    REPAIR_MUSIC_STEPS.has(ebikeStep) ||
+    REPAIR_MUSIC_STEPS.has(pylonStep) ||
+    REPAIR_MUSIC_STEPS.has(farmStep);
+
   useEffect(() => {
     const audio = AudioManager.getInstance();
-    audio.playMusic(GAME_MUSIC_PATH, GAME_MUSIC_VOLUME);
+    audio.playMusic(
+      inRepair ? REPAIR_MUSIC_PATH : GAME_MUSIC_PATH,
+      MUSIC_VOLUME,
+    );
+  }, [inRepair]);
 
+  useEffect(() => {
+    const audio = AudioManager.getInstance();
     return () => {
       audio.stopMusic();
     };