fix: resolve startup crash and CrashScreen button crashes (#127)

Two bugs caused the crash-at-startup report:

1. CrashScreen used the widget's build context (above its own MaterialApp)
   for ScaffoldMessenger.of() in button callbacks. When the screen is the
   root widget — the runApp() path after a startup crash — there is no
   ScaffoldMessenger above it, so both 'Copy to Clipboard' and 'Report Issue
   on Codeberg' crashed with a null check error. Fix: wrap Scaffold.body in
   Builder to obtain a context that is a descendant of the Scaffold.

2. path_provider_android 2.2.21 updated to Pigeon 26, which causes a
   channel-error on startup for some Android devices. Pin to <2.2.21
   (resolves to 2.2.20, which uses the stable pre-Pigeon-26 implementation).
   Additionally, make initDatabasePath() catch PlatformException so a
   channel error at the very start of main() no longer hard-crashes the app;
   _openConnection()'s lazy fallback retries after runApp() completes.

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

lib/data/db/database.dart

@@ -3,6 +3,7 @@ import 'dart:io';
 
 import 'package:drift/drift.dart';
 import 'package:drift/native.dart';
+import 'package:flutter/services.dart';
 import 'package:path/path.dart' as p;
 import 'package:path_provider/path_provider.dart';
 
@@ -578,9 +579,16 @@ String? _dbPath;
 
 /// Call after WidgetsFlutterBinding.ensureInitialized() so that the
 /// path_provider plugin channel is registered before the first DB access.
+/// On some Android versions the Pigeon channel is not ready at the very
+/// start of main(); if it fails, _openConnection() retries lazily.
 Future<void> initDatabasePath() async {
-  final dir = await getApplicationSupportDirectory();
-  _dbPath = p.join(dir.path, 'sharedinbox.db');
+  try {
+    final dir = await getApplicationSupportDirectory();
+    _dbPath = p.join(dir.path, 'sharedinbox.db');
+  } on PlatformException {
+    // Channel not yet established; LazyDatabase will resolve the path
+    // on first access, after runApp() completes initialization.
+  }
 }
 
 LazyDatabase _openConnection() {