Improve download location guidance and user experience

- Add download folder path detection based on platform
- Show download location in notification for first-time users
- Add helpful tooltip to download button explaining options
- Support Ctrl+click for "Save As" dialog option
- Add multi-line support for notification messages
- Provide guidance for changing browser download settings

Download UX improvements:
• Clear indication of where files are saved
• Platform-specific path information (Windows/Mac/Linux)
• First-time user education about download settings
• Keyboard shortcut support for advanced users

🤖 Generated with [Claude Code](https://claude.ai/code)

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

styles.css

@@ -670,7 +670,8 @@ header p {
     animation-fill-mode: forwards;
     box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
     word-wrap: break-word;
-    line-height: 1.4;
+    line-height: 1.5;
+    white-space: pre-line;
 }
 
 .notification.success {