frontend: Add DeviceClass views under a Devices sidebar section (DRA)

Is your feature request related to a problem? Please describe the impact that the lack of the feature requested is creating.

Dynamic Resource Allocation (resource.k8s.io/v1, stable since Kubernetes 1.34) has no views in Headlamp. To see which device classes a cluster offers, how they select devices or which driver config they apply, users have to read kubectl get deviceclasses -o yaml by hand.

This is the first slice of #4831, scoped to DeviceClass so the pattern can be reviewed on its own.

Describe the solution you'd like

• DeviceClass resource class (resource.k8s.io/v1, cluster scoped) registered in ResourceClasses and the plugin lib.
• A Devices sidebar section with Device Classes, plus /deviceclasses and /deviceclasses/:name routes, shown only when a selected cluster serves the API (same gating as the Scheduling section).
• List view (name, selectors, drivers, extended resource, age) and details view showing CEL selectors as text, a note when a class has no selectors (it matches every device), and driver parameters as JSON.
• A small reusable "which clusters serve this resource" helper for the remaining DRA kinds.
• Unit tests, stories/storyshots, i18n keys.

What users will benefit from this feature?

Operators running GPU/accelerator workloads through DRA on Kubernetes ≥ 1.34, on any Headlamp setup (desktop, in-cluster/Helm, multi-cluster). Plugin developers get the DeviceClass class via the plugin lib.

Are you able to implement this feature?

Yes (I will propose a PR). Part of my LFX Term 3 2026 mentorship on #4831 with @kannon92, @illume and @helayoty.

Additional context

Parent issue: #4831. ResourceClaim, Pod claim fields, ResourceClaimTemplate, ResourceSlice, claim details, map relations and beta capabilities follow in separate PRs.