feat(admin-members): add filterable members table

[bds165]

• Replaces the admin members HTML table with TanStack Table.
• Adds filters for years remaining, UoA student status, and returning/new member status.
• Integrates the existing delete member action into each row with confirmation without manual refresh.

[WilliamTayNZ]

Good work — all acceptance criteria met. TanStack wiring, filter controls, and delete integration all look correct. Nice touch hiding isConditionalReturningMember from the table with initialState.columnVisibility while still filtering on it.

One more thing before this merges:

Add an Edit link to the actions column. Chuan's edit member PR (#115) has been merged into feat/admin-auth, you'll have to pull the updated branch and merge it into your own, resolving any merge conflicts. As part of that, add an Edit link alongside the Delete button in the actions column in columns.tsx, linking to /admin/members/[id]/edit.