Add shared database helpers for async engines

[brothercorvo]

Summary

• add a shared reticulum_openapi.database module for URL normalisation, async engine/session creation, and schema initialisation hooks
• update the Emergency Management service to consume the shared helpers while keeping its backfill logic as an upgrade hook
• exercise the new helpers with integration tests that cover environment overrides, engine creation, and upgrade hook execution

Testing

• pytest tests/test_database_module.py tests/test_example_emergency_management.py

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Codex Task