Mount content, conversations, games, and contract readiness - #1677

Summary

• register ContentModule, ConversationsModule, and GamesModule in the live application
• add the root TypeORM configuration and migrations for content, conversations, messages, games, and players
• enforce conversation participant access and send idempotency keys from the messages client
• add authenticated game creation and game lookup endpoints
• include configured Soroban contracts in production readiness and export contract_health_up
• document the readiness probe and tighten frontend message/game types

Validation

• 4 focused backend test suites pass
• 91 focused tests pass
• focused backend and frontend lint checks report no errors
• repository-wide builds remain blocked by unrelated pre-existing errors

Closes #1545
Closes #1547
Closes #1548
Closes #1550