chore(knowledge): delete the dead base-card grid view

`BaseCard`/`BaseCardSkeleton`/`BaseCardSkeletonGrid` were the pre-redesign
grid-card knowledge base view, kept alive only by the barrel re-export —
no call sites since the Resource list replaced it.

Removing it orphans `components/constants.ts` entirely (its sort types
went with the dead sort; its three class-name constants had no consumers
left), so that goes too.

Author: waleedlatif1

apps/sim/app/workspace/[workspaceId]/knowledge/components/base-card/base-card.tsx

@@ -1,4 +1,3 @@
-export { BaseCard, BaseCardSkeleton, BaseCardSkeletonGrid } from './base-card'
 export { CreateBaseModal } from './create-base-modal'
 export { DeleteKnowledgeBaseModal } from './delete-knowledge-base-modal'
 export { EditKnowledgeBaseModal } from './edit-knowledge-base-modal'