Add fullscreen toggle and wake lock to prevent screen sleep

## Features
- Fullscreen button (⛶) in header to toggle fullscreen mode
- Wake Lock API integration to keep screen on while using the app
- Sun icon (☀) indicator shows wake lock status (bright = active)

## Wake Lock behavior
- Automatically requests wake lock when page loads
- Re-acquires wake lock when returning to the page
- Visual indicator pulses when active
- Gracefully hidden if Wake Lock API not supported

## Fullscreen
- Works on Android Chrome and desktop browsers
- iOS Safari has limited support (no fullscreen API)

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

web/index.html

@@ -33,6 +33,10 @@
                 <div class="status-dot"></div>
                 <span>Disconnected</span>
             </div>
+            <div class="wake-lock-status" id="wake-lock-status" title="Screen wake lock">
+                <span class="wake-icon">☀</span>
+            </div>
+            <button class="header-btn icon-btn" id="fullscreen-btn" onclick="app.toggleFullscreen()" title="Toggle fullscreen">⛶</button>
             <button class="header-btn secondary" onclick="app.refresh()">Refresh</button>
         </div>
     </header>