Add PWA, wake lock, and fullscreen to relay app

- Add wake lock (keep screen awake) functionality
- Add fullscreen toggle button
- Add dynamic PWA manifest generation
- Add favicon and icons for all relay pages
- Copy icons from main web folder

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

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

macropad-relay/public/index.html

@@ -4,6 +4,7 @@
     <meta charset="UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>MacroPad Relay</title>
+    <link rel="icon" type="image/png" href="/static/icons/favicon.png">
     <style>
         * {
             margin: 0;