Add CQRS read model pattern

[CosmicDreamer17]

Summary

• Adds read-only query side for both bounded contexts (CQRS separation)
• WorkItemReadModel and IntegrationJobReadModel as frozen dataclasses in application layer
• WorkItemQueryPort and IntegrationJobQueryPort abstract interfaces for read operations
• SqlAlchemyWorkItemQueryAdapter and SqlAlchemyIntegrationJobQueryAdapter concrete implementations
• Query functions: get_work_item, list_work_items, get_integration_job, list_integration_jobs with optional status filtering

Test plan

• 9 new query tests (53 total, all passing)
• Read models are frozen dataclasses (no mutation)
• Query functions use their own sessions (no UoW commit)
• Architecture enforcement still green (import-linter, pytest-archon)
• make all-checks passes

Closes #6

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