build(docker): warm prod cache at build time and add prod compose file

- Run cache:warmup in the build stage so containers start with a
  pre-built Symfony kernel and DI container
- Scope the cache volume to var/cache/prod/pools where Symfony writes
  pool data, preserving the warmed kernel across container restarts
- Add docker-compose.prod.yml for deploying the registry image without
  the dev override being picked up automatically
- Expand .dockerignore to exclude vendor/, tests/, docs, compose files,
  and env files from the build context

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Dockerfile

@@ -21,7 +21,9 @@ RUN composer install \
 # ── build stage (generate optimised classmap with source present) ──────────────
 FROM deps AS build
 COPY . .
-RUN composer dump-autoload --optimize --no-dev --no-interaction
+RUN composer dump-autoload --optimize --no-dev --no-interaction && \
+    mkdir -p var/cache var/log && \
+    APP_ENV=prod APP_SECRET=placeholder php bin/console cache:warmup --no-debug
 
 # ── dev stage (all deps + Xdebug, source is mounted at runtime) ───────────────
 FROM base AS dev
@@ -44,11 +46,11 @@ FROM base AS final
 RUN addgroup -S app && adduser -S -G app app
 
 COPY --from=build /app/vendor /app/vendor
+COPY --from=build /app/var/cache/prod /app/var/cache/prod
 COPY . .
 COPY docker/frankenphp/Caddyfile /etc/caddy/Caddyfile
 
-RUN mkdir -p var/cache var/log \
-    && chown -R app:app /app
+RUN mkdir -p var/cache/prod/pools var/log && chown -R app:app /app
 
 USER app