Add external link icons to messages

Implement CSS styles to display external link icons next to links in messages. Use a GitHub icon for GitHub links and a custom "W" icon for Wikipedia links to clearly indicate external sources. No modifications to JavaScript or TypeScript files were made.
[skip gpt_engineer]

Author: lovable-dev[bot]

src/index.css

@@ -73,18 +73,49 @@
 
 .chat-message a {
   @apply text-blue-300;
+  position: relative;
+  padding-right: 1.2em;
+}
 
-  &:hover {
-    @apply text-blue-600;
-  }
+/* External link icon for general links */
+.chat-message a[href^="http"]::after {
+  content: "↗";
+  position: absolute;
+  right: 0;
+  top: -0.1em;
+  font-size: 0.9em;
+  @apply text-muted-foreground;
+}
 
-  &:visited {
-    @apply text-purple-300;
-  }
+/* GitHub icon */
+.chat-message a[href*="github.com"]::after {
+  content: "G";
+  font-family: monospace;
+  font-weight: bold;
+  font-size: 0.8em;
+  top: 0;
+}
 
-  &:visited:hover {
-    @apply text-purple-600;
-  }
+/* Wikipedia icon */
+.chat-message a[href*="wikipedia.org"]::after {
+  content: "W";
+  font-family: "Times New Roman", serif;
+  font-style: italic;
+  font-weight: bold;
+  font-size: 0.9em;
+  top: 0;
+}
+
+.chat-message a:hover {
+  @apply text-blue-600;
+}
+
+.chat-message a:visited {
+  @apply text-purple-300;
+}
+
+.chat-message a:visited:hover {
+  @apply text-purple-600;
 }
 
 .chat-message > p {
@@ -199,3 +230,4 @@ details > details {
 .hljs-number {
   @apply text-orange-400;
 }
+