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/js/app.js

@@ -6,6 +6,7 @@ class MacroPadApp {
         this.tabs = [];
         this.currentTab = 'All';
         this.ws = null;
+        this.wakeLock = null;
 
         this.init();
     }
@@ -15,6 +16,7 @@ class MacroPadApp {
         await this.loadMacros();
         this.setupWebSocket();
         this.setupEventListeners();
+        this.setupWakeLock();
         this.checkInstallPrompt();
     }
 
@@ -245,6 +247,58 @@ class MacroPadApp {
         this.loadTabs();
         this.loadMacros();
     }
+
+    // Fullscreen
+    toggleFullscreen() {
+        if (!document.fullscreenElement) {
+            document.documentElement.requestFullscreen().catch(err => {
+                console.log('Fullscreen error:', err);
+            });
+        } else {
+            document.exitFullscreen();
+        }
+    }
+
+    // Wake Lock - prevents screen from sleeping
+    async setupWakeLock() {
+        if (!('wakeLock' in navigator)) {
+            console.log('Wake Lock API not supported');
+            document.getElementById('wake-lock-status')?.remove();
+            return;
+        }
+
+        // Request wake lock
+        await this.requestWakeLock();
+
+        // Re-acquire wake lock when page becomes visible again
+        document.addEventListener('visibilitychange', async () => {
+            if (document.visibilityState === 'visible') {
+                await this.requestWakeLock();
+            }
+        });
+    }
+
+    async requestWakeLock() {
+        try {
+            this.wakeLock = await navigator.wakeLock.request('screen');
+            this.updateWakeLockStatus(true);
+
+            this.wakeLock.addEventListener('release', () => {
+                this.updateWakeLockStatus(false);
+            });
+        } catch (err) {
+            console.log('Wake Lock error:', err);
+            this.updateWakeLockStatus(false);
+        }
+    }
+
+    updateWakeLockStatus(active) {
+        const status = document.getElementById('wake-lock-status');
+        if (status) {
+            status.classList.toggle('active', active);
+            status.title = active ? 'Screen will stay on' : 'Screen may sleep';
+        }
+    }
 }
 
 // Initialize app