fix(ebike): hide interact prompt while actively riding the bike

While the player is mounted on the e-bike and pressing a movement key,
the persistent 'Descendre du bike' prompt was visible on screen and
polluted the view during gameplay. The InteractableObject is now
unmounted as soon as window.ebikeDriveInputActive flips to true and
remounted the moment the bike comes to a stop.

The driving signal is read in a useFrame and only flips React state
on transitions, so this adds zero per-frame re-renders.

src/components/ebike/Ebike.tsx

@@ -358,6 +358,19 @@ export function Ebike({
         ? "Monter sur le bike"
         : "Descendre du bike";
 
+  // Hide the interact prompt while the player is actively riding the bike
+  // (driving input pressed) so the "Descendre du bike" label doesn't
+  // pollute the view. The prompt comes back the moment the bike comes to
+  // a stop. window.ebikeDriveInputActive is published every frame by
+  // PlayerController based on whether a movement key is currently held.
+  const [isEbikeDriving, setIsEbikeDriving] = useState(false);
+  useFrame(() => {
+    const driving =
+      movementMode === "ebike" && window.ebikeDriveInputActive === true;
+    if (driving !== isEbikeDriving) setIsEbikeDriving(driving);
+  });
+  const showInteractPrompt = !isEbikeDriving;
+
   const handleInteract = useCallback((): void => {
     if (window.ebikeBreakdownActive === true) return;
 
@@ -465,6 +478,7 @@ export function Ebike({
           {/* radius 20 → ~7 unités monde (scale 0.35).
               Sphère omnidirectionnelle pour que le raycast fonctionne
               quelle que soit l'orientation de la caméra (montée ou à pied). */}
+          {showInteractPrompt ? (
             <InteractableObject
               kind="trigger"
               label={interactionLabel}
@@ -481,6 +495,7 @@ export function Ebike({
                 />
               </mesh>
             </InteractableObject>
+          ) : null}
 
           {/* GPS + Speedmeter – same group so they are perfectly co-localised.
               GPS: full circle (Fresnel mask), renderOrder 10 000