[sparkle] chore: remove DataTableLoadingSkeleton - #32276

Description

Table skeletons should match the content of each cell. DataTableLoadingSkeleton encourages generic placeholders but cannot mimic details such as avatars, badges, or multiple text lines.

Remove the component, its export, and its stories. Replace its five usages with custom LoadingBlock compositions based on each table's actual cells, column widths, row heights, and responsive layout.

Tests

• LoadingBlock and scrollable table stories pass locally. The table story reports existing accessibility warnings; the application tables have no Storybook coverage.

Risk

• Low. Removes a Sparkle export; all repository callers are migrated.

Deploy Plan

• Publish Sparkle and deploy front.