Containerize frontend

Dockerfile

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+# Kaboot Frontend - Multi-stage Production Build
+#
+# Build:
+#   docker build \
+#     --build-arg VITE_API_URL=https://kaboot.example.com \
+#     --build-arg VITE_BACKEND_URL=https://kaboot.example.com \
+#     --build-arg VITE_AUTHENTIK_URL=https://auth.example.com \
+#     -t kaboot-frontend .
+
+FROM node:20-alpine AS builder
+WORKDIR /app
+
+COPY package*.json ./
+RUN npm ci --silent
+
+COPY index.html tsconfig.json vite.config.ts postcss.config.mjs ./
+COPY src/ ./src/
+COPY components/ ./components/
+COPY hooks/ ./hooks/
+COPY public/ ./public/
+
+ARG VITE_API_URL
+ARG VITE_BACKEND_URL
+ARG VITE_AUTHENTIK_URL
+ARG VITE_OIDC_CLIENT_ID=kaboot-spa
+ARG VITE_OIDC_APP_SLUG=kaboot
+ARG GEMINI_API_KEY
+
+ENV VITE_API_URL=$VITE_API_URL \
+    VITE_BACKEND_URL=$VITE_BACKEND_URL \
+    VITE_AUTHENTIK_URL=$VITE_AUTHENTIK_URL \
+    VITE_OIDC_CLIENT_ID=$VITE_OIDC_CLIENT_ID \
+    VITE_OIDC_APP_SLUG=$VITE_OIDC_APP_SLUG \
+    GEMINI_API_KEY=$GEMINI_API_KEY
+
+RUN npm run build
+
+FROM caddy:2-alpine
+COPY --from=builder /app/dist /srv/frontend
+EXPOSE 80 443
+CMD ["caddy", "run", "--config", "/etc/caddy/Caddyfile", "--adapter", "caddyfile"]