Serve the built SPA from the PHP image; drop the web container

The Dockerfile is now multi-stage: a Node stage runs `npm run build`, and the
PHP/Apache stage copies the result into public/. Apache + public/.htaccess route
/api* to the Slim front controller, serve real files, and fall back to
index.html for client-side routes.

docker-compose.yml loses the `web` service, its volume, and the source
bind-mount -- the image is the artifact now (rebuild to pick up changes).
Frontend dev moves to `npm run dev` on the host; APP_URL defaults to :8080 since
the one container serves both halves.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docker/apache.conf

@@ -5,7 +5,7 @@
         Options -Indexes +FollowSymLinks
         AllowOverride All
         Require all granted
-        DirectoryIndex index.php
+        DirectoryIndex index.html index.php
     </Directory>
 
     ErrorLog ${APACHE_LOG_DIR}/error.log