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/css/styles.css

@@ -550,3 +550,47 @@ body {
     color: white;
     padding: 0.5rem;
 }
+
+/* Fullscreen Button */
+.header-btn.icon-btn {
+    padding: 0.5rem 0.75rem;
+    font-size: 1.2rem;
+    line-height: 1;
+}
+
+/* Wake Lock Status */
+.wake-lock-status {
+    display: flex;
+    align-items: center;
+    padding: 0.25rem 0.5rem;
+    border-radius: 4px;
+    font-size: 1rem;
+    opacity: 0.4;
+    transition: opacity 0.3s;
+}
+
+.wake-lock-status.active {
+    opacity: 1;
+}
+
+.wake-lock-status .wake-icon {
+    color: #ffc107;
+}
+
+.wake-lock-status.active .wake-icon {
+    animation: pulse-glow 2s ease-in-out infinite;
+}
+
+@keyframes pulse-glow {
+    0%, 100% { opacity: 1; }
+    50% { opacity: 0.6; }
+}
+
+/* Fullscreen styles */
+:fullscreen .header {
+    padding-top: 0.5rem;
+}
+
+:fullscreen .macro-grid {
+    padding-bottom: 1rem;
+}