fix: QTE false race condition + restore auto-save slot in menu

- QTESystem: add if (!this.active) return guard in setInterval/setTimeout
  callbacks to prevent false result from firing after successful key press
- SaveLoadMenu: restore auto-save slot 0 row with blue styling, thumbnail,
  scene label, and read-only load button

engine/systems/QTESystem.ts

@@ -37,6 +37,7 @@ export class QTESystem {
     document.addEventListener('keydown', this.keyHandler)
 
     this.timerId = setInterval(() => {
+      if (!this.active) return
       const elapsed = Date.now() - startTime
       const remaining = Math.max(0, total - elapsed)
       onUpdate(remaining / 1000, qte.timeLimit)
@@ -47,6 +48,7 @@ export class QTESystem {
     }, this.tickMs)
 
     this.timeoutId = setTimeout(() => {
+      if (!this.active) return
       this.clear()
       onResult(false)
     }, total)