Implement functional admin panel

[kekehanshujun]

/claim #29

Summary

• Replaces the placeholder /admin page with a functional admin console for metrics, users, job moderation, disputes, platform controls, and append-only audit activity.
• Adds server-side admin-only enforcement after bearer-token auth for every /api/admin/* route.
• Adds paginated/filterable admin users, job moderation actions, dispute resolution, platform control updates, and audit log endpoints.
• Adds Zod validation, structured validation/not-found error responses, and focused API tests for authorization and admin workflows.
• Adds a Next proxy guard for /admin with opt-out demo mode for review environments.
• Verifies desktop and mobile layouts with browser screenshots; no horizontal overflow and no card/button overlap observed.

Validation

• npm test
• npm run build -w apps/web
• Browser check: /admin at 1365x900 and 390x844 viewports, with no horizontal overflow.

[BossChaos]

Code Review

PR: Implement functional admin panel by @kekehanshujun

• 🔒 Admin panel — needs security review

Wallet: 0xdaE5d307339074A24F579dB48e7c639359D94904

Code review for SecureBananaLabs bug-bounty