Refactor MariaDB role to stabilize initialization:

- Unify encoding/collation variables
- Improve connection logic for mysql_db module
- Switch to PyMySQL install path to avoid mysqlclient build failures
- Update healthcheck to container-friendly CMD-SHELL usage
- Normalize network and port configuration

These changes were applied during CI/CD pipeline debugging. The root CI/CD connectivity issue is still not fixed.

Reference: https://chatgpt.com/share/6931adf0-ce7c-800f-86f3-f867fbd3191f

roles/svc-db-mariadb/config/main.yml

@@ -11,6 +11,6 @@ docker:
       mem_reservation:    "2g"
       mem_limit:          "4g"
       pids_limit:         1024
-  network:              "mariadb"
+  network:                "mariadb"
   volumes:
-    data:               "mariadb_data"
+    data:                 "mariadb_data"