Cancel stale lookup scan fallback timer when closing popup

The setTimeout fallback in triggerLookupForSelectedWord was not being
tracked or cancelled, causing it to fire after test globals were
restored and hit an undefined document reference.

src/renderer/handlers/keyboard.ts

@@ -38,6 +38,7 @@ export function createKeyboardHandlers(
   let pendingSelectionAnchorAfterSubtitleSeek: 'start' | 'end' | null = null;
   let pendingLookupRefreshAfterSubtitleSeek = false;
   let resetSelectionToStartOnNextSubtitleSync = false;
+  let lookupScanFallbackTimer: ReturnType<typeof setTimeout> | null = null;
 
   const CHORD_MAP = new Map<
     string,
@@ -483,7 +484,9 @@ export function createKeyboardHandlers(
       });
     }
     // Fallback only if the explicit scan path did not open popup quickly.
-    setTimeout(() => {
+    if (lookupScanFallbackTimer !== null) clearTimeout(lookupScanFallbackTimer);
+    lookupScanFallbackTimer = setTimeout(() => {
+      lookupScanFallbackTimer = null;
       if (ctx.state.yomitanPopupVisible || isYomitanPopupVisible(document)) {
         return;
       }
@@ -523,6 +526,10 @@ export function createKeyboardHandlers(
       return false;
     }
 
+    if (lookupScanFallbackTimer !== null) {
+      clearTimeout(lookupScanFallbackTimer);
+      lookupScanFallbackTimer = null;
+    }
     dispatchYomitanPopupVisibility(false);
     dispatchYomitanFrontendClearActiveTextSource();
     clearNativeSubtitleSelection();