feat: wire RegistrationPage as app home, remove ScanPage

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/main.dart

@@ -1,5 +1,5 @@
 import 'package:flutter/material.dart';
-import 'package:pad_scanner/pages/scan_page.dart';
+import 'package:pad_scanner/pages/registration_page.dart';
 
 void main() {
   runApp(const PadScannerApp());
@@ -11,12 +11,12 @@ class PadScannerApp extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return MaterialApp(
-      title: 'PAD Scanner',
+      title: '上架登记',
       theme: ThemeData(
         colorScheme: ColorScheme.fromSeed(seedColor: Colors.blue),
         useMaterial3: true,
       ),
-      home: const ScanPage(),
+      home: const RegistrationPage(),
     );
   }
 }