[mohdTahaRafi]

Description

Adds src/tests/unit/use_deployments_test.tsx with 10 tests for useDeployments, using fake timers and a controllable document.hidden:

• first load, error message, the "Failed to fetch deployments" fallback, and aborted requests being ignored
• polling on the interval while the tab is visible, and no polling while it's hidden
• fetching again when the tab becomes visible, and on refetch()
• keeping the last list when a poll fails, and clearing the error on the next success
• aborting the request and stopping the timer on unmount

No app code changes. To check the tests actually catch regressions, I broke the hook four ways (polling while hidden, no visibility listener, not resetting the error, no abort on cleanup). Each one made exactly one test fail.

Test results: npm run unit is 152/152 (ran it three times to check the timer tests aren't flaky), and lint, format:check and typecheck pass. npm run test (Playwright) is 96/97. The one failure is dashboard.spec.ts:96, which also fails on master and is fixed in #61.

Fixes #64
Part of #20

Type of Change

• fix: Bug fix (non-breaking change which fixes an issue)
• feat: New feature (non-breaking change which adds functionality)
• refactor: Code refactor (no functional changes, no API changes)
• docs: Documentation update
• test: Adding or updating tests
• chore: Maintenance (CI, dependencies, tooling)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have linked the related issue above.
• My code follows the coding standards of this project.
• I have added tests that prove my fix is effective or my feature works.
• New and existing tests pass locally (npm run unit and npm run test).
• My changes generate no new lint warnings or errors (npm run lint).
• My PR title follows Conventional Commits (e.g., fix: resolve login redirect).

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[codxbrexx]

@mohdTahaRafi! Great work on the comprehensive test coverage and regression checks!

Appreciate the effort!