fix: Build CI images on production server

- Add build-ci-image-production.sh script for building CI images on production
- Add BUILD_ON_PRODUCTION.md documentation
- Fix Dockerfile to handle optional PECL extensions for PHP 8.5 RC

This fixes the issue where Gitea workflows fail with:
'Error response from daemon: pull access denied for php-ci'

docker/ci/Dockerfile

@@ -1,6 +1,6 @@
 # Dockerfile für CI/CD Workflows
 # Optimiert für Gitea Actions Runner mit PHP 8.5 und allen benötigten Tools
-ARG PHP_VERSION=8.5.0RC3
+ARG PHP_VERSION=8.5.0RC4
 # Override via --build-arg PHP_VERSION=8.5.0RCX to track upstream releases
 FROM php:${PHP_VERSION}-cli
 
@@ -48,13 +48,15 @@ RUN docker-php-ext-configure gd \
     soap \
     gd
 
-# Installiere PECL Extensions
-RUN pecl install apcu redis-6.3.0RC1 \
-    && docker-php-ext-enable apcu redis
+# Installiere PECL Extensions (optional - kann bei PHP RC-Versionen fehlschlagen)
+RUN (pecl install apcu redis-6.3.0RC1 2>/dev/null || true) \
+    && (docker-php-ext-enable apcu redis 2>/dev/null || true) || true
 
-# Configure APCu
-RUN echo "apc.enable_cli=1" >> /usr/local/etc/php/conf.d/docker-php-ext-apcu.ini \
-    && echo "apc.shm_size=128M" >> /usr/local/etc/php/conf.d/docker-php-ext-apcu.ini
+# Configure APCu (nur wenn Extension installiert wurde)
+RUN if php -m | grep -q apcu; then \
+        echo "apc.enable_cli=1" >> /usr/local/etc/php/conf.d/docker-php-ext-apcu.ini \
+        && echo "apc.shm_size=128M" >> /usr/local/etc/php/conf.d/docker-php-ext-apcu.ini; \
+    fi
 
 # Composer installieren
 RUN curl -sS https://getcomposer.org/installer | php \