feat: Add compass and region support

lib/services/region_scope_preferences.dart

@@ -0,0 +1,86 @@
+import 'dart:convert';
+import 'dart:typed_data';
+import 'package:crypto/crypto.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+import 'profiles_feature_service.dart';
+
+/// Stores per-channel region scope settings.
+///
+/// Each channel can optionally have a region scope assigned. When set, the app
+/// will set the flood scope on the device before sending channel messages so
+/// that repeaters outside the region won't forward them.
+class RegionScopePreferences {
+  static const String _namePrefix = 'region_scope_name_';
+  static const String _keyPrefix = 'region_scope_key_';
+
+  /// Get the saved scope for a channel.
+  /// Returns null if no scope is set.
+  static Future<({String name, Uint8List key})?> getScope(
+    int channelIdx,
+  ) async {
+    final prefs = await SharedPreferences.getInstance();
+    final name = prefs.getString(
+      ProfileStorageScope.scopedKey('$_namePrefix$channelIdx'),
+    );
+    final keyBase64 = prefs.getString(
+      ProfileStorageScope.scopedKey('$_keyPrefix$channelIdx'),
+    );
+    if (name == null || keyBase64 == null) return null;
+    try {
+      return (name: name, key: Uint8List.fromList(base64.decode(keyBase64)));
+    } catch (_) {
+      return null;
+    }
+  }
+
+  /// Save a region scope for a channel.
+  static Future<void> setScope(
+    int channelIdx,
+    String name,
+    Uint8List key,
+  ) async {
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.setString(
+      ProfileStorageScope.scopedKey('$_namePrefix$channelIdx'),
+      name,
+    );
+    await prefs.setString(
+      ProfileStorageScope.scopedKey('$_keyPrefix$channelIdx'),
+      base64.encode(key),
+    );
+  }
+
+  /// Clear the region scope for a channel.
+  static Future<void> clearScope(int channelIdx) async {
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.remove(
+      ProfileStorageScope.scopedKey('$_namePrefix$channelIdx'),
+    );
+    await prefs.remove(
+      ProfileStorageScope.scopedKey('$_keyPrefix$channelIdx'),
+    );
+  }
+
+  /// Clear all region scopes (all channels).
+  static Future<void> clearAllScopes() async {
+    final prefs = await SharedPreferences.getInstance();
+    final keys = prefs.getKeys();
+    for (final key in keys) {
+      if (key.contains(_namePrefix) || key.contains(_keyPrefix)) {
+        await prefs.remove(key);
+      }
+    }
+  }
+
+  /// Derive the 16-byte transport key for a region name.
+  ///
+  /// Matches firmware `TransportKeyStore::getAutoKeyFor`:
+  /// `SHA256("#regionname")` → first 16 bytes.
+  /// The name must include the leading `#` (auto-prepended if missing).
+  static Uint8List deriveRegionKey(String regionName) {
+    final normalized =
+        regionName.startsWith('#') ? regionName : '#$regionName';
+    final digest = sha256.convert(utf8.encode(normalized));
+    return Uint8List.fromList(digest.bytes.sublist(0, 16));
+  }
+}