feat(admin): ship guarded control panel

[devnull37]

/claim #29

Summary

• replace the admin placeholder with a real dashboard for metrics, users, moderation, disputes, controls, and audit logs
• add server-side admin enforcement and richer admin API routes
• support paginated/filterable admin data and action endpoints for user/listing/dispute/control flows
• add client-side admin guard, loading/error/empty states, accessible controls, and modular admin UI helpers
• tighten API error handling and add admin route tests

Verification

pm test

ode_modules\typescript\bin\tsc --noEmit -p apps\web\tsconfig.json