fix: use configured credentials for tenant schema cleanup

Same hardcoded dev credentials bug as InfrastructureService —
TenantDataCleanupService.dropPostgresSchema() used "cameleer"/"cameleer_dev"
instead of the provisioning properties, causing schema DROP to fail on
production installs during tenant deletion.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/main/java/net/siegeln/cameleer/saas/provisioning/TenantDataCleanupService.java

@@ -44,7 +44,7 @@ public class TenantDataCleanupService {
             return;
         }
 
-        try (Connection conn = DriverManager.getConnection(url, "cameleer", "cameleer_dev");
+        try (Connection conn = DriverManager.getConnection(url, props.datasourceUsername(), props.datasourcePassword());
              Statement stmt = conn.createStatement()) {
             stmt.execute("DROP SCHEMA IF EXISTS \"" + schema + "\" CASCADE");
             log.info("Dropped PostgreSQL schema: {}", schema);