feat: Improve chat message display

- Add sender name above outgoing messages in group chat
- Display emoji-only messages in larger font size
- Fix leading space before text in quoted replies

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/static/css/style.css

@@ -129,6 +129,13 @@ main {
     color: #6c757d;
 }
 
+.message-footer .message-sender.own {
+    font-weight: 600;
+    font-size: 0.875rem;
+    color: #084298;
+    margin-right: 0.5rem;
+}
+
 /* Message action buttons container */
 .message-actions {
     display: flex;
@@ -680,6 +687,12 @@ main {
     border-left-color: #084298;
 }
 
+/* Large Emoji for emoji-only messages */
+.emoji-large {
+    font-size: 2.5rem;
+    line-height: 1.2;
+}
+
 /* Clickable Links in Messages */
 .message-link {
     color: #0d6efd;