Add dimmed viewing mode via minimize button

- Minimize button now toggles a comfortable viewing filter
- Applies brightness(0.5) contrast(1.25) sepia(0.6)
- Smooth 0.3s transition between modes
- Persists choice in localStorage
- Creates warm, dimmed aesthetic while keeping XP theme

Click minimize to toggle between bright and dimmed modes.

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

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

static/style.css

@@ -37,6 +37,11 @@ body {
   background: teal;
   padding: 0;
   margin: 0;
+  transition: filter 0.3s ease;
+}
+
+body.dimmed {
+  filter: brightness(0.5) contrast(1.25) sepia(0.6);
 }
 
 /* Mobile responsiveness */