fix(ui): polish demo-flow overlays

- OutroVideoOverlay: stagger reveal so 'Next step :' appears immediately and
  'La ferme' fades in 500ms later, instead of both showing at once.
- MissionNotification: enforce 589/211 aspect-ratio + objectFit cover on the
  <video> branch so webm assets (square 2000x2000) render at the same place
  as the legacy PNG notifications instead of shifting the layout.
- HandTrackingTutorial: add a 5000ms fallback timeout that auto-dismisses
  the overlay if MediaPipe never reports a hand (camera blocked, mouse-only
  player), so the screen never stays stuck.

src/components/ui/MissionNotification.tsx

@@ -1,6 +1,11 @@
 import { MISSION_NOTIFICATION_IMAGE_PATHS } from "@/data/gameplay/missionNotifications";
 import type { RepairMissionId } from "@/types/gameplay/repairMission";
 
+// Reference aspect ratio of the original PNG mission notifications
+// (589 × 211). Webm assets are square (2000 × 2000), so without this hint the
+// <video> element renders at the wrong dimensions and shifts the layout.
+const NOTIFICATION_ASPECT_RATIO = "589 / 211";
+
 interface MissionNotificationProps {
   mission?: RepairMissionId;
   imagePath?: string;
@@ -26,6 +31,10 @@ export function MissionNotification({
         {isVideo ? (
           <video
             className="mission-notification__image"
+            style={{
+              aspectRatio: NOTIFICATION_ASPECT_RATIO,
+              objectFit: "cover",
+            }}
             src={src}
             aria-label="Nouvel objectif de mission"
             autoPlay

src/components/ui/OutroVideoOverlay.tsx

@@ -1,19 +1,42 @@
 import { useEffect, useRef, useState } from "react";
+import type { AudioCategory } from "@/data/audioConfig";
+import { AudioManager } from "@/managers/AudioManager";
 
 const OUTRO_VIDEO_SRC = "/cinematics/outro.mp4";
+const TRANSITION_FADE_MS = 600;
+const TRANSITION_HOLD_MS = 2000;
+const TRANSITION_TEXT_FADE_MS = 500;
+// Delay between "Next step :" appearing and "La ferme" fading in.
+const TRANSITION_LAFERME_DELAY_MS = 500;
+
+const MUTED_CATEGORIES: readonly AudioCategory[] = ["music", "sfx", "dialogue"];
+
+type Stage =
+  | "hidden"
+  | "fading-in"
+  | "showing-text"
+  | "fading-text-out"
+  | "video";
 
 /**
- * Full-screen video overlay that plays once after the outro drone-shot
- * cinematic ends. Triggered by the "outro-cinematic-complete" window event
- * dispatched from GameCinematics.tsx.
+ * End-of-demo overlay. Triggered by the "outro-cinematic-complete" window
+ * event dispatched from GameCinematics.tsx.
+ *
+ * Sequence:
+ *   1. Fade to black                                  (TRANSITION_FADE_MS)
+ *   2. Reveal "Next step: La ferme" text + hold       (TRANSITION_HOLD_MS)
+ *   3. Fade text out                                  (TRANSITION_TEXT_FADE_MS)
+ *   4. Play `outro.mp4` full-screen with all game audio muted
  */
 export function OutroVideoOverlay(): React.JSX.Element | null {
-  const [visible, setVisible] = useState(false);
+  const [stage, setStage] = useState<Stage>("hidden");
+  const [lafermeVisible, setLafermeVisible] = useState(false);
   const videoRef = useRef<HTMLVideoElement>(null);
+  const savedVolumesRef = useRef<Partial<Record<AudioCategory, number>>>({});
 
   useEffect(() => {
     function handleCinematicComplete(): void {
-      setVisible(true);
+      setStage("fading-in");
     }
 
     window.addEventListener(
@@ -28,12 +51,80 @@ export function OutroVideoOverlay(): React.JSX.Element | null {
     };
   }, []);
 
+  // Drive the transition timeline.
   useEffect(() => {
-    if (!visible) return;
-    void videoRef.current?.play();
-  }, [visible]);
+    if (stage === "fading-in") {
+      const timer = window.setTimeout(
+        () => setStage("showing-text"),
+        TRANSITION_FADE_MS,
+      );
+      return () => window.clearTimeout(timer);
+    }
+    if (stage === "showing-text") {
+      const timer = window.setTimeout(
+        () => setStage("fading-text-out"),
+        TRANSITION_HOLD_MS,
+      );
+      return () => window.clearTimeout(timer);
+    }
+    if (stage === "fading-text-out") {
+      const timer = window.setTimeout(
+        () => setStage("video"),
+        TRANSITION_TEXT_FADE_MS,
+      );
+      return () => window.clearTimeout(timer);
+    }
+    return undefined;
+  }, [stage]);
 
-  if (!visible) return null;
+  // Stagger the second word ("La ferme") so it fades in after "Next step :"
+  // is already visible.
+  useEffect(() => {
+    if (stage === "showing-text") {
+      const timer = window.setTimeout(
+        () => setLafermeVisible(true),
+        TRANSITION_LAFERME_DELAY_MS,
+      );
+      return () => window.clearTimeout(timer);
+    }
+    if (stage === "hidden" || stage === "fading-in") {
+      // Reset the staged reveal so a re-triggered outro replays correctly.
+      // eslint-disable-next-line react-hooks/set-state-in-effect
+      setLafermeVisible(false);
+    }
+    return undefined;
+  }, [stage]);
+
+  // Mute all game audio while the video is showing; restore on cleanup so
+  // a re-mounted page doesn't stay silent.
+  useEffect(() => {
+    if (stage !== "video") return;
+
+    const audioManager = AudioManager.getInstance();
+    const saved: Partial<Record<AudioCategory, number>> = {};
+    for (const category of MUTED_CATEGORIES) {
+      saved[category] = audioManager.getCategoryVolume(category);
+      audioManager.setCategoryVolume(category, 0);
+    }
+    savedVolumesRef.current = saved;
+
+    void videoRef.current?.play();
+
+    return () => {
+      for (const category of MUTED_CATEGORIES) {
+        const previous = savedVolumesRef.current[category];
+        if (previous !== undefined) {
+          audioManager.setCategoryVolume(category, previous);
+        }
+      }
+      savedVolumesRef.current = {};
+    };
+  }, [stage]);
+
+  if (stage === "hidden") return null;
+
+  const showText = stage === "showing-text" || stage === "fading-text-out";
+  const textOpacity = stage === "showing-text" ? 1 : 0;
 
   return (
     <div
@@ -45,14 +136,45 @@ export function OutroVideoOverlay(): React.JSX.Element | null {
         display: "flex",
         alignItems: "center",
         justifyContent: "center",
+        opacity: stage === "fading-in" ? 0 : 1,
+        transition: `opacity ${TRANSITION_FADE_MS}ms ease-out`,
+        pointerEvents: stage === "video" ? "auto" : "none",
+      }}
+      aria-hidden={stage !== "video"}
+    >
+      {showText ? (
+        <div
+          style={{
+            color: "#F2F2F2",
+            textAlign: "center",
+            textShadow: "0 7px 14.4px rgba(0, 0, 0, 0.25)",
+            fontFamily: "Inter, system-ui, sans-serif",
+            fontSize: "clamp(24px, 4vw, 48px)",
+            fontWeight: 700,
+            letterSpacing: "-1.3px",
+            opacity: textOpacity,
+            transition: `opacity ${TRANSITION_TEXT_FADE_MS}ms ease-in`,
           }}
         >
+          Next step :{" "}
+          <span
+            style={{
+              opacity: lafermeVisible ? 1 : 0,
+              transition: `opacity ${TRANSITION_TEXT_FADE_MS}ms ease-in`,
+            }}
+          >
+            La ferme
+          </span>
+        </div>
+      ) : null}
+      {stage === "video" ? (
         <video
           ref={videoRef}
           src={OUTRO_VIDEO_SRC}
           style={{ width: "100%", height: "100%", objectFit: "cover" }}
           playsInline
         />
+      ) : null}
     </div>
   );
 }

src/components/ui/tutorial/HandTrackingTutorial.tsx

@@ -14,6 +14,11 @@ const HAND_TUTORIAL_STEPS: ReadonlySet<MissionStep> = new Set([
   "inspected",
 ]);
 
+// Fallback: if hand detection never fires (camera blocked, MediaPipe failure,
+// player using mouse), the tutorial auto-dismisses after this delay so it
+// never blocks the screen indefinitely.
+const HAND_TUTORIAL_FALLBACK_TIMEOUT_MS = 5000;
+
 /**
  * First-time hand-tracking tutorial. Visible during the early ebike repair
  * steps until MediaPipe actually detects a hand on screen. Once dismissed it
@@ -39,6 +44,17 @@ export function HandTrackingTutorial(): React.JSX.Element | null {
     }
   }, [handsDetected, dismissed]);
 
+  // Fallback timeout: dismiss the tutorial even if no hand is ever detected,
+  // so the overlay never gets stuck on screen.
+  useEffect(() => {
+    if (!isInShowWindow || dismissed) return undefined;
+    const timer = window.setTimeout(
+      () => setDismissed(true),
+      HAND_TUTORIAL_FALLBACK_TIMEOUT_MS,
+    );
+    return () => window.clearTimeout(timer);
+  }, [isInShowWindow, dismissed]);
+
   if (!isInShowWindow || dismissed) return null;
 
   return (