Add localization support for German, Spanish, French, and Italian

- Updated localization files for French, Croatian, Italian, Slovenian to include translations for German, Spanish, French, and Italian.
- Added new methods for handling drawing messages sent to the public channel in multiple languages.
- Enhanced the Contact model to identify public channels using a dedicated method.
- Implemented echo detection for public channel messages, including tracking and reporting of echoes.
- Updated BLE response handling to support echo detection and tracking of sent messages.
- Modified UI components to reflect new localization strings and echo statuses.

lib/models/sent_message_tracker.dart

@@ -0,0 +1,83 @@
+import 'dart:typed_data';
+
+/// Tracks sent public channel messages for echo detection
+///
+/// When a message is sent to the public channel, it's encrypted with AES128-ECB
+/// which is deterministic. When another node receives and rebroadcasts it,
+/// the raw packet will be byte-for-byte identical. We can detect these echoes
+/// by comparing the raw packet data from PUSH_CODE_LOG_RX_DATA (0x88) against
+/// packets we've sent.
+class SentMessageTracker {
+  /// Unique identifier for the message (timestamp-based)
+  final String messageId;
+
+  /// SHA256 hash of the encrypted packet for fast O(1) lookup
+  final String packetHashHex;
+
+  /// Original raw encrypted packet bytes (for verification)
+  final Uint8List? rawPacket;
+
+  /// When the message was sent
+  final DateTime sentTime;
+
+  /// When this tracker expires (default: 5 minutes)
+  final DateTime expiryTime;
+
+  /// Number of times we've detected this message being rebroadcast
+  int echoCount;
+
+  /// Unique echo paths detected (SNR/RSSI signatures)
+  /// Format: "snr_rssi" e.g., "20_-56" means SNR=5.0dB (20/4), RSSI=-56dBm
+  final Set<String> uniqueEchoPaths;
+
+  /// Timestamps when echoes were detected
+  final List<DateTime> echoTimestamps;
+
+  SentMessageTracker({
+    required this.messageId,
+    required this.packetHashHex,
+    this.rawPacket,
+    required this.sentTime,
+    required this.expiryTime,
+    this.echoCount = 0,
+    Set<String>? uniqueEchoPaths,
+    List<DateTime>? echoTimestamps,
+  })  : uniqueEchoPaths = uniqueEchoPaths ?? {},
+        echoTimestamps = echoTimestamps ?? [];
+
+  /// Check if this tracker has expired
+  bool get isExpired => DateTime.now().isAfter(expiryTime);
+
+  /// Time until expiry
+  Duration get timeUntilExpiry => expiryTime.difference(DateTime.now());
+
+  /// Add an echo detection
+  void addEcho(int snrRaw, int rssiDbm) {
+    echoCount++;
+    uniqueEchoPaths.add('${snrRaw}_$rssiDbm');
+    echoTimestamps.add(DateTime.now());
+  }
+
+  /// Get the SNR in dB from raw value
+  static double snrRawToDb(int snrRaw) {
+    return snrRaw.toSigned(8) / 4.0;
+  }
+
+  /// Get formatted echo statistics
+  String get echoStats {
+    if (echoCount == 0) return 'No echoes detected';
+    if (echoCount == 1) return '1 echo from ${uniqueEchoPaths.length} path(s)';
+    return '$echoCount echoes from ${uniqueEchoPaths.length} path(s)';
+  }
+
+  /// Get average time to first echo
+  Duration? get timeToFirstEcho {
+    if (echoTimestamps.isEmpty) return null;
+    return echoTimestamps.first.difference(sentTime);
+  }
+
+  @override
+  String toString() {
+    return 'SentMessageTracker(id=$messageId, echoes=$echoCount, paths=${uniqueEchoPaths.length}, expired=$isExpired)';
+  }
+}