test(frontend): add unit tests for PublicProjectService

[Ma77Ball]

What changes were proposed in this PR?

• Adds public-project.service.spec.ts covering PublicProjectService; no production code changed.
• Verifies the getType (text), makePublic, makePrivate, list and add endpoints, methods and bodies.
• Covers the empty-list edge case for addPublicProjects.

Any related issues, documentation, discussions?

Closes: #6452

How was this PR tested?

• Run cd frontend && npx nx test gui --include="**/public-project.service.spec.ts", expect 7 passed.
• Full frontend suite runs in CI via yarn test:ci, selected by the auto-applied frontend label.

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

Co-authored with Claude Opus 4.8 in compliance with ASF

[github-actions]

Automated Reviewer Suggestions

Based on the git blame history of the changed files, we recommend the following reviewers:

• No candidates found from git blame history.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.18%. Comparing base (c7473a1) to head (2521412).
⚠️ Report is 12 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6464      +/-   ##
============================================
- Coverage     70.20%   70.18%   -0.03%     
  Complexity     3390     3390              
============================================
  Files          1142     1143       +1     
  Lines         44844    44853       +9     
  Branches       4949     4950       +1     
============================================
- Hits          31484    31481       -3     
- Misses        11725    11738      +13     
+ Partials       1635     1634       -1     

Flag	Coverage Δ		*Carryforward flag
access-control-service	70.00% <ø> (ø)		Carriedforward from c7473a1
agent-service	76.76% <ø> (ø)		Carriedforward from c7473a1
amber	66.68% <ø> (ø)		Carriedforward from c7473a1
computing-unit-managing-service	9.97% <ø> (ø)		Carriedforward from c7473a1
config-service	52.30% <ø> (ø)		Carriedforward from c7473a1
file-service	65.63% <ø> (ø)		Carriedforward from c7473a1
frontend	68.93% <ø> (-0.04%)	⬇️
notebook-migration-service	78.94% <ø> (ø)		Carriedforward from c7473a1
pyamber	91.19% <ø> (ø)		Carriedforward from c7473a1
workflow-compiling-service	55.14% <ø> (ø)		Carriedforward from c7473a1

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

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[Ma77Ball]

/request-review @Yicong-Huang

[Yicong-Huang]

I think we don't need to maintain it: project has been deprecated.