feat: P2 - QTE system, subtitles, save thumbnails

- QTESystem: trigger detection via timeupdate, multi-key matching, timeout handling
- QTEOverlay: SVG countdown ring + key prompts + success/fail animation
- Engine: integrate QTE (timeupdate check, conditional branching, effect application)
- Subtitles: WebVTT parsing + synchronized subtitle rendering
- GamePlayer: overlay QTE and subtitle components
- SaveSystem: DB v2 with thumbnail field, canvas snapshot at 320x180 JPEG
- SaveLoadMenu: thumbnail preview for save slots
- VideoManager: getActiveVideoElement() for canvas capture
- App.vue: QTE/subtitle integration, thumbnail capture on save
- stores: QTE state management, save list with thumbnails
- demo.json: QTE scene (right_door), subtitles, new event types
- ROADMAP: mark P2 as completed

src/composables/useGameEngine.ts

@@ -47,6 +47,22 @@ export function useGameEngine(videoEls: () => [HTMLVideoElement | null, HTMLVide
       store.setGameEnded(true)
       engine.choiceSystem.stop()
     })
+
+    engine.on('qteTrigger', (qte) => {
+      store.showQTE(qte)
+    })
+
+    engine.on('qteTimer', ({ remaining }) => {
+      store.updateQTE(remaining)
+    })
+
+    engine.on('qteResult', ({ success }) => {
+      store.resolveQTE(success)
+    })
+
+    engine.videoManager.onTimeUpdate((t: number) => {
+      store.setVideoTime(t)
+    })
   }
 
   function start() {
@@ -73,12 +89,31 @@ export function useGameEngine(videoEls: () => [HTMLVideoElement | null, HTMLVide
 
   async function saveGame(slot: number) {
     const state = engine.stateManager
+    const currentScene = store.currentScene
+
+    // Capture thumbnail from active video
+    let thumbnail: string | undefined
+    try {
+      const video = engine.videoManager.getActiveVideoElement()
+      if (video && video.readyState >= 2) {
+        const canvas = document.createElement('canvas')
+        canvas.width = 320
+        canvas.height = 180
+        const ctx = canvas.getContext('2d')
+        if (ctx) {
+          ctx.drawImage(video, 0, 0, 320, 180)
+          thumbnail = canvas.toDataURL('image/jpeg', 0.6)
+        }
+      }
+    } catch { /* ignore canvas errors */ }
+
     await saveSystem.save(slot, {
       timestamp: Date.now(),
-      currentScene: store.currentScene?.id ?? '',
+      currentScene: currentScene?.id ?? '',
       variables: state.variables,
       flags: [...state.flags],
       history: state.history,
+      thumbnail,
     })
     await refreshSaves()
   }