[scanner] fix: add timer cleanup to prevent memory leaks

[kubestellar-hive]

Fixes #19857

Adds proper cleanup for setInterval/setTimeout calls in 4 test/component files to prevent memory leaks during test runs.

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✅ Test Coverage Check

All new source files in this PR have corresponding test files.

Checked web/src/hooks/ and web/src/components/ against origin/main.

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✅ Post-Merge Verification: passed

Commit: 019483c09dde6a579ad7d062a0322c51f059f058
Specs run: mission-import.spec.ts smoke.spec.ts
Report: https://github.com/kubestellar/console/actions/runs/28337812327

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Post-merge build verification passed ✅

Both Go and frontend builds compiled successfully against merge commit 019483c09dde6a579ad7d062a0322c51f059f058.