docs(cache): add comprehensive cache configuration and permission handling guides

- Introduce `cache-configuration.md` for detailed instructions on cache setup, permission troubleshooting, and best practices.
- Add `cache-permissions-quick-fix.md` for concise resolutions to common permission errors.
- Include a detailed `FILECACHE_PERMISSION_FIX_PLAN.md` outlining solutions for permission-related issues.
- Enhance `docker-entrypoint.sh` with permission fixes for multi-user caches.
- Update `Makefile` with cache clear commands for local and staging environments.
- Improve `FileCache` for graceful degradation on permission errors, ensuring reliability under multi-user scenarios.

docker/php/docker-entrypoint.sh

@@ -27,6 +27,8 @@ mkdir -p /var/www/html/storage/analytics 2>/dev/null || true
 mkdir -p /var/www/html/storage/sessions 2>/dev/null || true
 
 # Fix ownership for all storage directories (including mounted volumes)
+# WICHTIG: Cache-Verzeichnis ben?tigt 775 (Group-writable) f?r Multi-User/Process-Umgebungen
+# F?r das L?schen von Cache-Dateien werden nur Verzeichnis-Rechte ben?tigt, nicht Datei-Rechte
 if [ -d /var/www/html/storage ]; then
     chown -R appuser:appuser /var/www/html/storage 2>/dev/null || true
     chmod -R 775 /var/www/html/storage 2>/dev/null || true