feat: update Docker configuration for improved performance and add local environment example

Dockerfile

@@ -1,18 +1,15 @@
-FROM node:22-alpine AS base
+# node:22-slim (Debian/glibc) is ~2x faster for Next.js builds vs Alpine/musl
+FROM node:22-slim AS base
 RUN corepack enable && corepack prepare pnpm@latest --activate
 WORKDIR /app
 
-# --- Install + Build in one stage ---
+# --- Install + Build ---
 FROM base AS builder
-# CACHE_BUST: change this value to force a full rebuild (busts Docker layer cache)
-ARG CACHE_BUST=14
-RUN echo "Cache bust: ${CACHE_BUST}"
 COPY . .
-RUN pnpm install --no-frozen-lockfile
+RUN --mount=type=cache,id=pnpm,target=/root/.local/share/pnpm/store \
+    pnpm install --no-frozen-lockfile --prefer-offline
 ENV NEXT_TELEMETRY_DISABLED=1
 
-# NEXT_PUBLIC_* vars are baked into the Next.js build at compile time.
-# Pass them as build args so the same Dockerfile works for any environment.
 ARG NEXT_PUBLIC_CI=false
 ARG NEXT_PUBLIC_SITE_URL=https://myeasycms.de
 ARG NEXT_PUBLIC_SUPABASE_URL=http://localhost:8000
@@ -35,17 +32,16 @@ ENV NEXT_PUBLIC_STRIPE_PUBLISHABLE_KEY=${NEXT_PUBLIC_STRIPE_PUBLISHABLE_KEY}
 ENV NEXT_PUBLIC_BILLING_PROVIDER=${NEXT_PUBLIC_BILLING_PROVIDER}
 RUN pnpm --filter web build
 
-# --- Run ---
-FROM base AS runner
+# --- Run (slim for smaller image than full Debian) ---
+FROM node:22-slim AS runner
+RUN corepack enable && corepack prepare pnpm@latest --activate
 WORKDIR /app
 ENV NODE_ENV=production
 ENV NEXT_TELEMETRY_DISABLED=1
 
 COPY --from=builder /app/ ./
 
-RUN addgroup --system --gid 1001 nodejs && adduser --system --uid 1001 nextjs
-
-# Ensure Next.js cache directories are writable by the nextjs user
+RUN groupadd --system --gid 1001 nodejs && useradd --system --uid 1001 nextjs
 RUN mkdir -p /app/apps/web/.next/cache && chown -R nextjs:nodejs /app/apps/web/.next/cache
 
 USER nextjs