Increase unit test coverage across the codebase

[cynthiabondi]

Related PRs: #1198

Summary
Add comprehensive unit test coverage across ViewModels, repositories, and use cases that were previously untested.

Motivation
Large portions of the codebase have no unit tests, making refactoring risky and regressions hard to catch in CI.

Acceptance criteria

• Add unit tests for untested ViewModels, repos, and use cases
• CI runs only release unit tests (for speed)
• All new and existing tests pass

References
Closes #1198

[cynthiabondi]

Completed in #1198