[TASK] Remove underline from Cancel buttons in all views

[jenny-s51]

Certification

• I certify I am an Epic Owner for Kubeflow Notebooks 2.0 and expected to create planning-related issues.

Description

UX feedback per @tobiastal - update Cancel button styling to match PF patterns:

Acceptance Criteria

• All Cancel button instances have underline removed
• Cancel buttons match PF standard cancel action style
• Consistent styling across all forms and modals

[jenny-s51]

/area frontend
/area v2

[jenny-s51]

Closed via #737