fix: return focus to message input after sending

Added FocusNode to TextField, requestFocus() after send completes.
Also autofocus=true so cursor is in the input when entering a room.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/features/chat/presentation/message_input.dart

@@ -52,6 +52,7 @@ class MessageInput extends StatefulWidget {
 
 class _MessageInputState extends State<MessageInput> {
   final _controller = TextEditingController();
+  final _focusNode = FocusNode();
   bool _hasText = false;
   bool _isPickingFile = false;
 
@@ -67,6 +68,7 @@ class _MessageInputState extends State<MessageInput> {
   @override
   void dispose() {
     _controller.dispose();
+    _focusNode.dispose();
     super.dispose();
   }
 
@@ -75,6 +77,8 @@ class _MessageInputState extends State<MessageInput> {
     if (text.isEmpty) return;
     _controller.clear();
     await widget.onSend(text);
+    // Return focus to the input so the user can keep typing.
+    _focusNode.requestFocus();
   }
 
   Future<void> _pickFile() async {
@@ -180,6 +184,8 @@ class _MessageInputState extends State<MessageInput> {
                   Expanded(
                     child: TextField(
                       controller: _controller,
+                      focusNode: _focusNode,
+                      autofocus: true,
                       decoration: const InputDecoration(
                         hintText: 'Message',
                         contentPadding: EdgeInsets.symmetric(