feat(chat): Optimize chat input and message bubble rendering

lib/features/chat/widgets/modern_chat_input.dart

@@ -1340,9 +1340,7 @@ class _ModernChatInputState extends ConsumerState<ModernChatInput>
     // For compact mode, render text field shell with floating buttons on sides
     if (showCompactComposer) {
       // Build the text field shell
-      Widget textFieldShell = AnimatedContainer(
-        duration: const Duration(milliseconds: 180),
-        curve: Curves.easeOutCubic,
+      Widget textFieldShell = Container(
         padding: const EdgeInsets.symmetric(horizontal: Spacing.md),
         constraints: const BoxConstraints(minHeight: TouchTarget.input),
         decoration: shellDecoration,
@@ -1404,9 +1402,7 @@ class _ModernChatInputState extends ConsumerState<ModernChatInput>
     }
 
     // For expanded mode with quick pills, use the full shell
-    Widget shell = AnimatedContainer(
-      duration: const Duration(milliseconds: 180),
-      curve: Curves.easeOutCubic,
+    Widget shell = Container(
       decoration: shellDecoration,
       child: ConstrainedBox(
         constraints: BoxConstraints(

lib/features/chat/widgets/user_message_bubble.dart

@@ -498,6 +498,12 @@ class _UserMessageBubbleState extends ConsumerState<UserMessageBubble> {
     final inlineEditFill = context.conduitTheme.surfaceContainer.withValues(
       alpha: 0.92,
     );
+    // Use rounded rectangle for multiline, pill for single-line (like chat input)
+    // Consider multiline if text exceeds ~50 chars or contains newlines
+    // Check length first (O(1)) to short-circuit before scanning for newlines
+    final content = widget.message.content;
+    final isMultiline = content.length > 50 || content.contains('\n');
+    final bubbleRadius = isMultiline ? AppBorderRadius.xl : AppBorderRadius.pill;
 
     return GestureDetector(
       onLongPress: () => _showMessageMenu(context),
@@ -539,9 +545,7 @@ class _UserMessageBubbleState extends ConsumerState<UserMessageBubble> {
                         ),
                         decoration: BoxDecoration(
                           color: context.conduitTheme.chatBubbleUser,
-                          borderRadius: BorderRadius.circular(
-                            AppBorderRadius.messageBubble,
-                          ),
+                          borderRadius: BorderRadius.circular(bubbleRadius),
                         ),
                         child: _isEditing
                             ? Focus(