fix(docker): restore runtime NEXT_PUBLIC vars, add DEFAULT_LOCALE build arg

- Restore NEXT_PUBLIC_SUPABASE_URL + NEXT_PUBLIC_SUPABASE_PUBLIC_KEY at runtime
  (server code reads from process.env — needs these for SSR)
- Use external URL (API_EXTERNAL_URL) for both build and runtime
- Add NEXT_PUBLIC_DEFAULT_LOCALE=de as Dockerfile build arg so next-intl
  compiles with the correct default locale (was falling back to 'en')
- CACHE_BUST=3 to force full rebuild

Dockerfile

@@ -4,7 +4,7 @@ WORKDIR /app
 
 # --- Install + Build in one stage ---
 FROM base AS builder
-ARG CACHE_BUST=2
+ARG CACHE_BUST=3
 COPY . .
 RUN pnpm install --no-frozen-lockfile
 ENV NEXT_TELEMETRY_DISABLED=1
@@ -14,9 +14,11 @@ ENV NEXT_TELEMETRY_DISABLED=1
 ARG NEXT_PUBLIC_SITE_URL=https://myeasycms.de
 ARG NEXT_PUBLIC_SUPABASE_URL=http://localhost:8000
 ARG NEXT_PUBLIC_SUPABASE_PUBLIC_KEY
+ARG NEXT_PUBLIC_DEFAULT_LOCALE=de
 ENV NEXT_PUBLIC_SITE_URL=${NEXT_PUBLIC_SITE_URL}
 ENV NEXT_PUBLIC_SUPABASE_URL=${NEXT_PUBLIC_SUPABASE_URL}
 ENV NEXT_PUBLIC_SUPABASE_PUBLIC_KEY=${NEXT_PUBLIC_SUPABASE_PUBLIC_KEY}
+ENV NEXT_PUBLIC_DEFAULT_LOCALE=${NEXT_PUBLIC_DEFAULT_LOCALE}
 RUN pnpm --filter web build
 
 # --- Run ---