security: comprehensive security audit and remediation (20 fixes)

CRITICAL fixes:
- Restrict X-View-Tenant impersonation to global admin only (was any admin)
- Add authorization to subscription endpoints (was open to any user)
- Make webhook signature verification mandatory (was skippable)
- Remove databaseName from JWT payload (resolve server-side with cache)
- Reduce body size limit from 1GB to 10MB (50MB for bulk CFDI)
- Restrict .env file permissions to 600

HIGH fixes:
- Add authorization to SAT cron endpoints (global admin only)
- Add Content-Security-Policy and Permissions-Policy headers
- Centralize isGlobalAdmin() utility with caching
- Add rate limiting on auth endpoints (express-rate-limit)
- Require authentication on logout endpoint

MEDIUM fixes:
- Replace Math.random() with crypto.randomBytes for temp passwords
- Remove console.log of temporary passwords in production
- Remove DB credentials from admin notification email
- Add escapeHtml() to email templates (prevent HTML injection)
- Add file size validation on FIEL upload (50KB max)
- Require TLS for SMTP connections
- Normalize email to lowercase before uniqueness check
- Remove hardcoded default for FIEL_ENCRYPTION_KEY

Also includes:
- Complete production deployment documentation
- API reference documentation
- Security audit report with remediation details
- Updated README with v0.5.0 changelog
- New client admin email template
- Utility scripts (create-carlos, test-emails)
- PM2 ecosystem config updates

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/api/package.json

@@ -46,6 +46,7 @@
     "@types/node-forge": "^1.3.14",
     "@types/nodemailer": "^7.0.11",
     "@types/pg": "^8.18.0",
+    "express-rate-limit": "^8.3.1",
     "prisma": "^5.22.0",
     "tsx": "^4.19.0",
     "typescript": "^5.3.0"