Add functional admin panel

[sypham98-prog]

/claim #29

Summary

• Replaced the placeholder admin page with a guarded operations panel covering metrics, trust distribution, users, moderation, disputes, platform controls, and audit logs.
• Added server-side admin authorization to every /api/admin/* route and implemented paginated/filterable admin endpoints.
• Added admin actions for user suspension/reinstatement/bans, listing moderation decisions, dispute rulings/refunds/escalation, control toggles with confirmation, notifications, and append-only audit entries.
• Added detail views for user profiles, active jobs, dispute history, dispute thread/evidence, and transaction data.

Validation

• npm test
• npm run build -w apps/web
• node --check apps/api/src/services/adminService.js apps/api/src/controllers/adminController.js apps/api/src/routes/adminRoutes.js apps/api/src/middleware/auth.js apps/api/src/tests/admin.test.js
• git diff --check

Demo walkthrough

1. Start the API and web app locally.
2. Use an admin JWT containing role: "admin" as ff_access_token, then open /admin.
3. Refresh the dashboard, filter users/audit logs, view a user profile, moderate a flagged listing, inspect a dispute, issue a ruling/refund, and toggle platform controls.
4. Confirm each action appears in the audit log.

Notes

• Non-admin requests are redirected from /admin and rejected by the API with 403.
• This implementation is scoped to the repository's current mock/in-memory service architecture.
• AI assistance was used to implement and validate this PR.

[sypham98-prog]

Withdrawing this PR from my active bounty queue because the bounty instructions require a short demo video, and I am filtering out video-required bounties going forward. Thanks for the review.