chore(ci): add Docker BuildKit examples, .dockerignore, CI cache docs; tune vite config

aether_container_env/Dockerfile.buildkit.example

@@ -0,0 +1,27 @@
+## BuildKit-friendly multi-stage Dockerfile example for Aether frontend
+
+# Stage 1: dependencies
+FROM node:20-alpine AS deps
+WORKDIR /app
+COPY package.json package-lock.json ./
+RUN npm ci --no-audit --prefer-offline
+
+# Stage 2: build
+FROM node:20-alpine AS build
+WORKDIR /app
+# optionally reuse deps from previous stage
+COPY --from=deps /app/node_modules ./node_modules
+COPY . .
+# If you want to use BuildKit cache mounts during local development, uncomment the next line
+# RUN --mount=type=cache,target=/root/.npm npm ci
+RUN npm run build
+
+# Stage 3: runtime (static site served by nginx)
+FROM nginx:stable-alpine AS runtime
+COPY --from=build /app/build /usr/share/nginx/html
+EXPOSE 80
+CMD ["nginx", "-g", "daemon off;"]
+
+# Notes:
+# - Keep dependency installation separate from copying source to maximize cache hits when only application code changes.
+# - For backend images, follow the same pattern: install deps early, copy source later, and keep a small final runtime image.