Add web-app with machine-specific builds

Implements per-machine customization for web-app deployment:
- Shared web-app source code deployed to all machines
- Machine-specific .env files and images
- Build helper script to assemble and build on target machines

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

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

web-app/package.json

@@ -0,0 +1,8 @@
+{
+  "name": "web-app",
+  "version": "1.0.0",
+  "description": "Example web application",
+  "scripts": {
+    "build": "echo 'Building web-app...' && mkdir -p dist && cp -r public dist/ && cp .env dist/"
+  }
+}