[P2] Enforce data integrity and harden container startup

[apple050620312]

Summary

• Recover safely from find-or-create uniqueness races without masking unrelated database failures.
• Add a migration that deduplicates existing rows and enforces unique member and custom-domain constraints.
• Expand and index event names for operational queries.
• Flush buffered analytics and close HTTP sessions during shutdown.
• Generate runtime configuration safely, bound database startup waits, and make migrations explicit and fail-closed.
• Keep the database private to the Compose network and add a one-shot migration service.

Priority

P2 — improves correctness, rollout safety, and recovery under concurrent multi-worker operation.

Validation

• Migration imports successfully.
• Compose migration topology and private database assertions pass.
• Runtime imports and all Python AST parsing checks pass.