fix: use configured credentials for infrastructure PostgreSQL queries

pgConnection() had hardcoded dev credentials ("cameleer"/"cameleer_dev")
instead of using the provisioning properties, causing "password
authentication failed" on production installs where the password is
generated.

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

src/main/java/net/siegeln/cameleer/saas/vendor/InfrastructureService.java

@@ -271,7 +271,7 @@ public class InfrastructureService {
     // --- Private helpers ---
 
     private Connection pgConnection() throws SQLException {
-        return DriverManager.getConnection(props.datasourceUrl(), "cameleer", "cameleer_dev");
+        return DriverManager.getConnection(props.datasourceUrl(), props.datasourceUsername(), props.datasourcePassword());
     }
 
     private Connection chConnection() throws SQLException {