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/index.html

@@ -13,7 +13,7 @@
       <div class="title-bar">
         <div class="title-bar-text">This Little Corner — Elastic Search</div>
         <div class="title-bar-controls">
-          <button aria-label="Minimize"></button>
+          <button id="minimizeBtn" aria-label="Minimize"></button>
           <button aria-label="Maximize"></button>
           <button aria-label="Close"></button>
         </div>