Add new friends system, and sharing legs support

lib/components/login/login.dart

@@ -294,6 +294,7 @@ class _RegisterPanelContentState extends State<RegisterPanelContent> {
   final _passwordController = TextEditingController();
   final _inviteController = TextEditingController();
   bool _registering = false;
+  String? _usernameError;
 
   @override
   void dispose() {
@@ -306,10 +307,21 @@ class _RegisterPanelContentState extends State<RegisterPanelContent> {
   }
 
   Future<void> _register() async {
+    final username = _usernameController.text.trim();
+    if (username.contains(' ') || username.contains('@')) {
+      setState(() {
+        _usernameError = 'Username cannot contain spaces or @';
+      });
+      return;
+    } else {
+      setState(() {
+        _usernameError = null;
+      });
+    }
     setState(() => _registering = true);
     try {
       await widget.authService.register(
-        username: _usernameController.text.trim(),
+        username: username,
         email: _emailController.text.trim(),
         fullName: _displayNameController.text.trim(),
         password: _passwordController.text,
@@ -363,7 +375,22 @@ class _RegisterPanelContentState extends State<RegisterPanelContent> {
             border: OutlineInputBorder(),
             labelText: "Username",
           ),
+          onChanged: (_) {
+            if (_usernameError != null &&
+                !_usernameController.text.contains(' ') &&
+                !_usernameController.text.contains('@')) {
+              setState(() => _usernameError = null);
+            }
+          },
         ),
+        if (_usernameError != null)
+          Padding(
+            padding: const EdgeInsets.only(top: 4.0),
+            child: Text(
+              _usernameError!,
+              style: TextStyle(color: Theme.of(context).colorScheme.error),
+            ),
+          ),
         const SizedBox(height: 8),
         TextField(
           controller: _displayNameController,