debug: Add debug logging for Google Drive upload issues

Added debug logging to:
1. main.dart - Log IS_PRO_VERSION value at startup
2. main_screen.dart - Log IS_PRO_VERSION and isBusiness in screen build
3. pdf_preview_screen.dart - Log PDF Drive upload process with file ID verification

This will help diagnose why Google Drive uploads appear to succeed but files
are not visible in Drive.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

lib/main.dart

@@ -20,7 +20,10 @@ const bool isProVersion = bool.fromEnvironment('IS_PRO_VERSION', defaultValue: t
 
 void main() async {
   WidgetsFlutterBinding.ensureInitialized();
-  
+
+  // 🔍 DEBUG: Check IS_PRO_VERSION flag
+  debugPrint('🔍 IS_PRO_VERSION = $isProVersion');
+
   // Initialize Hive
   await Hive.initFlutter();
   

lib/screens/main_screen.dart

@@ -46,6 +46,9 @@ class _MainScreenState extends ConsumerState<MainScreen> {
     final isBusiness = userProfile.isBusinessMode;
     final t = Translations(userProfile.locale); // Translation helper
 
+    // 🔍 DEBUG: Check IS_PRO_VERSION flag
+    debugPrint('🔍 MainScreen: IS_PRO_VERSION = $isProVersion, isBusiness = $isBusiness');
+
     // Define Screens for each mode
     // Pro版かLite版かで画面を切り替え
     final List<Widget> screens = isBusiness

lib/screens/pdf_preview_screen.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import 'package:flutter/foundation.dart'; // debugPrint
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:printing/printing.dart';
 import 'package:pdf/pdf.dart';
@@ -284,7 +285,8 @@ class PdfPreviewScreen extends ConsumerWidget {
         ..name = fileName
         ..mimeType = 'application/pdf';
 
-      await driveApi.files.create(
+      debugPrint('[PDF_DRIVE] 📤 アップロード開始: $fileName (${bytes.length} bytes)');
+      final uploadedFile = await driveApi.files.create(
         driveFile,
         uploadMedia: drive.Media(
           Stream.value(bytes.toList()),
@@ -292,6 +294,13 @@ class PdfPreviewScreen extends ConsumerWidget {
         ),
       );
 
+      if (uploadedFile.id == null) {
+        debugPrint('[PDF_DRIVE] ❌ アップロード失敗: ID取得不可');
+        throw Exception('アップロードに失敗しました（IDなし）');
+      }
+
+      debugPrint('[PDF_DRIVE] ✅ アップロード完了: ID=${uploadedFile.id}');
+
       // 5. Success notification
       if (context.mounted) {
         ScaffoldMessenger.of(context).showSnackBar(