Add auto-growing textarea for chat input

- Textarea now automatically expands as user types multiline messages
- Resets to minimum height after message is sent
- CSS: Set min-height (60px) and max-height (400px) with auto overflow
- Removed fixed rows attribute to allow dynamic height
- Disabled manual resize to prevent user confusion
- Provides better UX for composing longer messages

static/css/style.css

@@ -123,6 +123,11 @@ html, body {
     background-color: var(--bg-secondary);
     color: var(--text-primary);
     transition: background-color 0.3s ease, border-color 0.3s ease;
+    min-height: 60px;
+    max-height: 400px;
+    overflow-y: auto;
+    resize: none;
+    box-sizing: border-box;
 }
 
 /* Styling for the message body wrapper that contains header and content */