feat: production deployment - full update with providers, admin, glossaries, pricing, tests

Major changes across backend, frontend, infrastructure:
- Provider system with model selection (Google, DeepL, OpenAI, Ollama, Google Cloud)
- Admin panel: user management, pricing, settings
- Glossary system with CSV import/export
- Subscription and tier quota management
- Security hardening (rate limiting, API key auth, path traversal fixes)
- Docker compose for dev, prod, and IONOS deployment
- Alembic migrations for new tables
- Frontend: dashboard, pricing page, landing page, i18n (en/fr)
- Test suite and verification scripts

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/app/admin/constants.ts

@@ -1,4 +1,4 @@
-import { LayoutDashboard, Users, Settings, FileText, Key, type LucideIcon } from 'lucide-react';
+import { CreditCard, LayoutDashboard, Settings, FileText, Users, type LucideIcon } from 'lucide-react';
 
 export interface AdminNavItem {
   label: string;
@@ -9,7 +9,8 @@ export interface AdminNavItem {
 export const adminNavItems: AdminNavItem[] = [
   { label: 'Dashboard', href: '/admin', icon: LayoutDashboard },
   { label: 'Users', href: '/admin/users', icon: Users },
-  { label: 'Providers', href: '/admin/settings', icon: Key },
+  { label: 'Pricing & Stripe', href: '/admin/pricing', icon: CreditCard },
+  { label: 'Providers', href: '/admin/settings', icon: Settings },
   { label: 'System', href: '/admin/system', icon: Settings },
   { label: 'Logs', href: '/admin/logs', icon: FileText },
 ];