Add unit and integration tests for contracts, adapters, and persistence

[KSemenenko]

Problem

The control-plane backlog introduces many new contracts and adapters that need real automated verification as they land.

Scope

• Track unit and integration tests for domain contracts, provider adapters, and persistence flows
• Keep tests focused on real contracts and caller-visible behavior
• Align with existing repo testing rules

Out of scope

• UI automation flows that belong in the Uno.UITests issue
• CI workflow changes beyond what later validation issues cover

Implementation notes

• Keep tests meaningful and implementation-driving
• Ensure persistence and adapter flows are covered early
• Preserve the repo rule against placeholder tests

Definition of Done

• The issue defines the first test-growth areas clearly
• Later implementation can add tests in step with feature delivery

Verification

• Review the issue against the AGENTS testing policy and planned runtime issues

Dependencies

• Parent epic: [Epic] Expand automated validation for the control-plane product #21