feat: Implement accessible SFTP file browser and native editor

lib/services/ssh_service.dart

@@ -110,6 +110,39 @@ class SshService {
     }
   }
 
+  // --- SFTP Operations ---
+
+  Future<SftpClient> _getSftpClient() async {
+    if (_client == null) throw Exception('Not connected');
+    return await _client!.sftp();
+  }
+
+  Future<List<SftpName>> listDirectory(String path) async {
+    final sftp = await _getSftpClient();
+    return await sftp.listdir(path);
+  }
+
+  Future<String> readFile(String path) async {
+    final sftp = await _getSftpClient();
+    
+    // Check file size first
+    final stat = await sftp.stat(path);
+    if ((stat.size ?? 0) > 1024 * 1024) { // 1MB limit
+      throw Exception('File is too large to edit (Max 1MB).');
+    }
+
+    final file = await sftp.open(path);
+    final content = await file.readBytes();
+    return utf8.decode(content);
+  }
+
+  Future<void> writeFile(String path, String content) async {
+    final sftp = await _getSftpClient();
+    final file = await sftp.open(path, mode: SftpFileOpenMode.create | SftpFileOpenMode.write | SftpFileOpenMode.truncate);
+    await file.writeBytes(utf8.encode(content));
+    await file.close();
+  }
+
   void write(String data) {
     if (_session != null) {
       _session!.write(utf8.encode(data));