feat(tutorial): add movement and hand-tracking onboarding overlays

Mount two first-time tutorial overlays driven by the game state machine:

- MovementTutorial: visible during the intro reveal and the free-walk
  step before the ebike mount, dismissed on the first Z/Q/S/D keydown.
- HandTrackingTutorial: visible during the early ebike repair steps
  (fragmented, scanning, inspected), dismissed when MediaPipe detects
  any hand on screen.

Both share a generic TutorialOverlay shell (transparent panel, dark
blue border, lucide-react Hand / inline ZQSD keycap icons, centered
text). The overlay sits at z-index 14, behind Subtitles (15) and
the talkie overlay (16), so dialogue/subtitle UI stays in front.

Dismissals stay persistent for the session: keyboard-triggered uses
event-handler setState; hand-detection uses a guarded effect-driven
setState (same pattern as PylonDownedPylon resync).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/ui/tutorial/MovementTutorial.tsx

@@ -0,0 +1,57 @@
+import { useEffect, useState } from "react";
+import { useGameStore } from "@/managers/stores/useGameStore";
+import type { GameStep } from "@/types/game";
+import { TutorialOverlay } from "@/components/ui/tutorial/TutorialOverlay";
+
+const MOVEMENT_KEYS = new Set(["z", "q", "s", "d"]);
+// Intro steps where the movement tutorial is allowed to display. From the
+// reveal fade through the free-walk window before the ebike mount.
+const MOVEMENT_TUTORIAL_STEPS: ReadonlySet<GameStep> = new Set([
+  "reveal",
+  "await-ebike-mount",
+]);
+
+function KeyCap({ label }: { label: string }): React.JSX.Element {
+  return <span className="tutorial-overlay__keycap">{label}</span>;
+}
+
+/**
+ * First-time movement tutorial. Visible during the intro reveal and the
+ * walk-around step before the ebike mount, until the player presses any
+ * of Z, Q, S, D. Once dismissed it stays dismissed for the session.
+ */
+export function MovementTutorial(): React.JSX.Element | null {
+  const introStep = useGameStore((state) => state.intro.currentStep);
+  const [dismissed, setDismissed] = useState(false);
+
+  const isInShowWindow = MOVEMENT_TUTORIAL_STEPS.has(introStep);
+
+  useEffect(() => {
+    if (dismissed) return;
+    function onKeyDown(event: KeyboardEvent): void {
+      if (MOVEMENT_KEYS.has(event.key.toLowerCase())) {
+        setDismissed(true);
+      }
+    }
+    window.addEventListener("keydown", onKeyDown);
+    return () => window.removeEventListener("keydown", onKeyDown);
+  }, [dismissed]);
+
+  if (!isInShowWindow || dismissed) return null;
+
+  return (
+    <TutorialOverlay
+      icon={
+        <div className="tutorial-overlay__keyboard">
+          <span aria-hidden="true" />
+          <KeyCap label="Z" />
+          <span aria-hidden="true" />
+          <KeyCap label="Q" />
+          <KeyCap label="S" />
+          <KeyCap label="D" />
+        </div>
+      }
+      text="Utilisez le clavier et la souris pour vous déplacer."
+    />
+  );
+}