fix: copy PHP files before composer install (classmap needs them)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker/Dockerfile

@@ -14,14 +14,12 @@ RUN apk add --no-cache nginx supervisor
 # Composer
 COPY --from=composer:2 /usr/bin/composer /usr/bin/composer
 
-# Backend PHP deps (separate layer so code changes don't bust cache)
+# Backend PHP files + deps
 WORKDIR /var/www/html/lux-studio/api
+COPY backend/*.php ./
 COPY backend/composer.json ./
 RUN composer install --no-dev --optimize-autoloader --no-interaction --no-security-blocking
 
-# Backend PHP files
-COPY backend/*.php ./
-
 # Built frontend
 COPY --from=builder /build/dist /var/www/html/lux-studio