test: unit tests for LandingPageComponent

[Ma77Ball]

What changes were proposed in this PR?

• Add landing-page.component.spec.ts covering creation, the constructor's userChanged() subscription (login/logout transitions update isLogin and currentUid), ngOnInit calling both getWorkflowCount and loadTops, count population from HubService.getCount, the three top-loved buckets populated by loadTops, the loadTops error path logging via console.error, getTopLovedEntries enriching items via SearchService.extendSearchResultsWithHubActivityInfo(items, true, ["access"]) per action and returning a map keyed by action, and navigateToSearch routing for "workflow", "dataset", and unknown types.
• Stub HubService, SearchService, WorkflowPersistService, and DatasetService; reuse StubUserService for a real userChanged() subject; replace Router.navigate with a vitest spy.

Any related issues, documentation, or discussions?

Closes: #5225

How was this PR tested?

• Ran yarn ng test --watch=false --include='src/app/hub/component/landing-page/landing-page.component.spec.ts', 10/10 tests pass.
• Ran yarn format:fix (1 file formatted, 505 unchanged).

Was this PR authored or co-authored using generative AI tooling?

Co-authored with Claude Opus 4.7 in compliance with ASF

[Ma77Ball]

/request-review @aicam

[aicam]

LGTM!

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 48.63%. Comparing base (d5bc8b7) to head (5f8bdbc).

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #5234      +/-   ##
============================================
- Coverage     48.72%   48.63%   -0.10%     
- Complexity     2375     2379       +4     
============================================
  Files          1044     1044              
  Lines         40096    40037      -59     
  Branches       4252     4257       +5     
============================================
- Hits          19538    19471      -67     
- Misses        19411    19415       +4     
- Partials       1147     1151       +4     

Flag	Coverage Δ		*Carryforward flag
access-control-service	39.53% <ø> (ø)		Carriedforward from 8a7366f
agent-service	33.76% <ø> (ø)		Carriedforward from 8a7366f
amber	51.58% <ø> (+0.02%)	⬆️	Carriedforward from 8a7366f
computing-unit-managing-service	0.00% <ø> (ø)		Carriedforward from 8a7366f
config-service	0.00% <ø> (ø)		Carriedforward from 8a7366f
file-service	37.99% <ø> (ø)		Carriedforward from 8a7366f
frontend	40.20% <ø> (+0.17%)	⬆️
python	90.46% <ø> (-0.34%)	⬇️	Carriedforward from 8a7366f
workflow-compiling-service	56.81% <ø> (ø)		Carriedforward from 8a7366f

*This pull request uses carry forward flags. Click here to find out more.

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