Security hardening: 12 improvements across the stack
1. env.ts: APP_KEY placeholder detection with validation
2. schema.prisma: password column widened to varchar(255) for argon2id
3. auth.ts: trustHost restricted to development only
4. next.config.ts: added CSP, HSTS, X-Frame-Options, and other security headers
5. api.ts: CORS restricted to APP_URL instead of wildcard
6. register-form.tsx: migrated from REST API fetch to server action (useActionState)
7. twofactor.ts + 2fa page: TOTP recovery codes (8 one-time codes, generated and displayed)
8. register.ts: password min length 8 + complexity requirements (upper, lower, digit)
9. register.ts + help-tickets.ts + radio-shouts.ts: Zod schema validation
10. rate-limit.ts: improved periodic cleanup with aggressive eviction at 10k buckets
11. guard.ts + admin actions: rate-limited admin actions (30 req/min per staff)
12. help-tickets.ts + radio-shouts.ts: content moderation via moderateOrThrow