Solr local: same layout as prod (configsets from solr_cores), service solr-new renamed solr

- image pinned to solr:8.10.1, SOLR_HOME=/var/solr/data, solr_cores mounted ro on /opt/configsets
- update_solr_config.sh writes into a solr_cores tree and RELOADs cores
- solr_cores bumped to configset restructure, solr_cores_stage worktree ignored

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitignore

@@ -9,4 +9,5 @@ solr_data/*
 var_solr/*
 ressources/xdebug.ini
 ressources/*.sql.gz
-ai-docs/
+ai-docs/
+solr_cores_stage/