fix: eliminate UX flash by calling setStrings() immediately in observer

The 100ms pure-debounce approach caused a visible layout flash on every
render (normal mode too) because Tokyo UX was not applied for 100ms.

Fix: call setStrings() immediately in the MutationObserver callback to
prevent any flash, AND keep a 250ms delayed follow-up call to catch
async train re-renders from mock XHR setTimeout(0) responses.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

lib/webViewInjectjavascript.ts

@@ -1258,10 +1258,12 @@ const textInsert = new MutationObserver( (mutations) =>{
     const currentLines = document.querySelector('#topHeader div').innerText;
     window.ReactNativeWebView.postMessage(JSON.stringify({type:"currentLines",currentLines}));
   }
-  // Debounced setStrings: fires after any subtree change settles.
-  // This catches async train re-renders (e.g. from mock XHR setTimeout(0)).
+  // Apply Tokyo UX immediately (prevents visible flash on normal renders).
+  try { setStrings(); } catch(e) {}
+  // Also schedule a follow-up after 250ms to catch async re-renders
+  // triggered by mock XHR setTimeout(0) responses that settle later.
   clearTimeout(_ssDebounce);
-  _ssDebounce = setTimeout(() => { try { setStrings(); } catch(e) {} }, 100);
+  _ssDebounce = setTimeout(() => { try { setStrings(); } catch(e) {} }, 250);
 });
 
 // 監視を開始 (subtree: true で深い子孫の変化も捕捉する)