refactor(cloudbuild): migrate components to Backstage UI

[tobiasp284]

Hey, I just made a Pull Request!

Important

This is stacked on #10264. Until that PR merges, GitHub shows its migration commit here as well. The UI-specific change is commit 21d0b7972.

Migrates the Cloud Build plugin's UI from direct Material UI v4 usage to the Backstage UI design system.

• replaces the workflow history table with the Backstage UI table and pagination
• migrates cards, loading/error states, typography, layout, actions, and tooltips
• replaces Material UI icons with Remix icons
• replaces makeStyles with CSS Modules
• removes direct @material-ui/core and @material-ui/icons dependencies
• preserves the existing run links, timestamps, reload, rerun, details, and entity-card behavior

Verification

• yarn tsc:full
• yarn lint
• yarn test plugins/cloudbuild --watchAll=false
• yarn build:api-reports plugins/cloudbuild
• no direct Material UI imports remain in the plugin source

✔️ Checklist

• A changeset describing the change and affected packages.
• Added or updated documentation (not applicable; installation is unchanged)
• Tests for new functionality and regression tests for bug fixes
• Screenshots attached (draft; visual verification pending)
• All commits have a Signed-off-by line in the message.