feat: update chat layout and session management

- Added max-width to chat controls and session select for better layout.
- Increased CHAT_SESSIONS_ACTIVE_MINUTES from 10 to 120 for extended session duration.
- Changed brand logo source to a local favicon for improved asset management.

ui/src/styles/chat/layout.css

@@ -295,6 +295,7 @@
 
 .chat-controls__session {
   min-width: 140px;
+  max-width: 420px;
 }
 
 .chat-controls__thinking {
@@ -361,6 +362,9 @@
 .chat-controls__session select {
   padding: 6px 10px;
   font-size: 13px;
+  max-width: 420px;
+  overflow: hidden;
+  text-overflow: ellipsis;
 }
 
 .chat-controls__thinking {