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/src/controllers/fiel.controller.ts

@@ -16,6 +16,18 @@ export async function upload(req: Request, res: Response): Promise<void> {
       return;
     }
 
+    // Validate file sizes (typical .cer/.key files are under 10KB, base64 ~33% larger)
+    const MAX_FILE_SIZE = 50_000; // 50KB base64 ≈ ~37KB binary
+    if (cerFile.length > MAX_FILE_SIZE || keyFile.length > MAX_FILE_SIZE) {
+      res.status(400).json({ error: 'Los archivos FIEL son demasiado grandes (máx 50KB)' });
+      return;
+    }
+
+    if (password.length > 256) {
+      res.status(400).json({ error: 'Contraseña FIEL demasiado larga' });
+      return;
+    }
+
     const result = await uploadFiel(tenantId, cerFile, keyFile, password);
 
     if (!result.success) {