style: change system message color to red for error visibility

DO NOT MERGE - This is a demo PR for visual demonstration purposes only.

Changes the system_message() style from TEXT_MUTED (gray) to ERROR (red #FF6B6B)
to display backend JSON error messages in red color.

Author: echobt

src/cortex-core/src/style.rs

@@ -362,11 +362,11 @@ impl CortexStyle {
         Style::default().fg(SKY_BLUE)
     }
 
-    /// System message style: muted italic text
+    /// System message style: error red italic text for backend error messages
     #[inline]
     pub fn system_message() -> Style {
         Style::default()
-            .fg(TEXT_MUTED)
+            .fg(ERROR)
             .add_modifier(Modifier::ITALIC)
     }