feat: display cover image on dataset detail page

[xuang7]

What changes were proposed in this PR?

This PR adds cover image support to the dataset detail page header.

• If a dataset does not have a cover image, a default placeholder is displayed.
• If a dataset has a cover image, the uploaded image is displayed at 280×120

Demo

Any related issues, documentation, discussions?

Related to #4319

How was this PR tested?

Passed existing automated tests.

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

Generated-by: Claude Opus 4.7

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 42.61%. Comparing base (7bb102e) to head (28c6ea9).

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #5060      +/-   ##
============================================
- Coverage     42.85%   42.61%   -0.24%     
+ Complexity     2207     2178      -29     
============================================
  Files          1045     1045              
  Lines         40146    39936     -210     
  Branches       4240     4215      -25     
============================================
- Hits          17203    17019     -184     
+ Misses        21878    21864      -14     
+ Partials       1065     1053      -12     

Flag	Coverage Δ		*Carryforward flag
access-control-service	39.53% <ø> (ø)		Carriedforward from 62d4489
agent-service	33.72% <ø> (ø)		Carriedforward from 62d4489
amber	43.22% <ø> (-0.52%)	⬇️	Carriedforward from 62d4489
computing-unit-managing-service	0.00% <ø> (ø)		Carriedforward from 62d4489
config-service	0.00% <ø> (ø)		Carriedforward from 62d4489
file-service	32.18% <ø> (ø)		Carriedforward from 62d4489
frontend	33.93% <ø> (ø)
python	88.89% <ø> (-0.11%)	⬇️	Carriedforward from 62d4489
workflow-compiling-service	47.72% <ø> (ø)		Carriedforward from 62d4489

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

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