Keep .env and local build artifacts out of the Docker image

Without a .dockerignore, COPY . . baked the .env file (including the
webhook secret) into the image and overwrote the container's
node_modules with the host's. Pass public build-time values as build
args and provide the rest at runtime through env_file.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docker-compose.yml

@@ -1,7 +1,15 @@
 services:
   uiogaming.no:
     container_name: uiogaming.no
-    build: .
+    build:
+      context: .
+      # Values are read from .env
+      args:
+        NEXT_PUBLIC_SANITY_PROJECT_ID: ${NEXT_PUBLIC_SANITY_PROJECT_ID}
+        NEXT_PUBLIC_SANITY_DATASET: ${NEXT_PUBLIC_SANITY_DATASET}
+        NEXT_PUBLIC_UMAMI_SRC: ${NEXT_PUBLIC_UMAMI_SRC}
+        NEXT_PUBLIC_UMAMI_WEBSITE_ID: ${NEXT_PUBLIC_UMAMI_WEBSITE_ID}
+    env_file: .env
     ports:
       - 9000:9000
     environment: