Split admin/+page.svelte (573 lines) into:
- UsersTab.svelte: user table with delete action
- TagsTab.svelte: tag list with inline rename and delete
- GroupsTab.svelte: groups table with inline edit + create form
- SystemTab.svelte: backfill buttons with own state
Page drops from 573 → ~40 lines.
Part of #75
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
