test(frontend): add unit tests for DatasetFileSelectorComponent

[yangzhang75]

What changes were proposed in this PR?

Adds a unit test spec for DatasetFileSelectorComponent, which previously had no *.spec.ts. The component is a Formly field type whose onClickOpenFileSelectionModal() opens a dataset-selection modal and writes the chosen path back into the form control when the modal closes with a value.

Any related issues, documentation, discussions?

Closes #5471

How was this PR tested?

New unit tests added in dataset-file-selector.component.spec.ts, run via ng test (Vitest). They cover:

• component creation
• onClickOpenFileSelectionModal() opens the dataset selection modal exactly once
• a selected path is written back into the form control
• the form control is left unchanged when the modal is dismissed without a path
• isFileSelectionEnabled reflects the GUI config

All 5 tests pass; eslint and prettier checks are clean.

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

Generated-by: Claude Code

[xuang7]

LGTM!

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 52.20%. Comparing base (564ccdb) to head (f33241f).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #5576      +/-   ##
============================================
+ Coverage     52.17%   52.20%   +0.02%     
  Complexity     2482     2482              
============================================
  Files          1068     1068              
  Lines         41311    41311              
  Branches       4439     4439              
============================================
+ Hits          21556    21565       +9     
+ Misses        18490    18480      -10     
- Partials       1265     1266       +1     

Flag	Coverage Δ		*Carryforward flag
access-control-service	64.61% <ø> (ø)		Carriedforward from 564ccdb
agent-service	33.76% <ø> (ø)		Carriedforward from 564ccdb
amber	53.28% <ø> (ø)		Carriedforward from 564ccdb
computing-unit-managing-service	1.65% <ø> (ø)		Carriedforward from 564ccdb
config-service	56.06% <ø> (ø)		Carriedforward from 564ccdb
file-service	38.32% <ø> (ø)		Carriedforward from 564ccdb
frontend	46.47% <ø> (+0.05%)	⬆️
pyamber	90.72% <ø> (ø)		Carriedforward from 564ccdb
python	90.75% <ø> (ø)		Carriedforward from 564ccdb
workflow-compiling-service	58.69% <ø> (ø)		Carriedforward from 564ccdb

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

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