Fix integration test database isolation

[havlli]

Summary

• reset the shared Testcontainers PostgreSQL database before each integration test
• reseed default embed type and roles after cleanup
• run Flyway migrations in the shared test container setup

Verification

• mvn -ntp -B verify
• GitHub Actions Test Coverage manual run passed: https://github.com/havlli/EventPilot/actions/runs/24941524013

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

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