feat(admin): build leadership admin dashboard

[cdcore09]

Summary

Build an admin dashboard for board members and staff to manage the membership, view analytics, and perform administrative actions.

Requirements

Member Management

• Member directory with search, sort, and filter
• View full member details (all profile fields + internal metadata)
• Add members manually (invite by email)
• Remove/deactivate members with reason
• Edit member roles (promote to admin, demote)
• Bulk actions (export, role changes)

Analytics & Visualization

• Member growth chart (line chart: members over time)
• Institution breakdown (bar chart: top institutions by member count)
• Geographic distribution (if location data available)
• Working group participation (which groups are most active)
• New members per month trend
• Retention metrics (active vs inactive)

Data Export

• Export member list as CSV
• Configurable columns (select which fields to export)
• Date range filtering for exports

Audit Log

• View all admin actions (who did what, when)
• Filter by action type, admin user, date range
• Log entries for: role changes, member removal, manual additions

Context

Parent issue: #1916
Depends on: #1917 (schema), #1918 (auth — admin role required), #1919 (profiles — member data to display)

Implementation Notes

• Route: /admin with sub-routes (/admin/members, /admin/analytics, /admin/audit)
• Charts: Recharts or @visx (both work well with React + Tailwind)
• Dashboard layout: sidebar nav + main content (different from the public site layout)
• Must be fully protected — only admin and super_admin roles can access
• Consider real-time updates via polling or WebSocket for active member counts