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/providers/ThemeProvider.tsx

@@ -0,0 +1,11 @@
+"use client";
+
+import * as React from "react";
+import { ThemeProvider as NextThemesProvider } from "next-themes";
+
+export function ThemeProvider({
+  children,
+  ...props
+}: React.ComponentProps<typeof NextThemesProvider>) {
+  return <NextThemesProvider {...props}>{children}</NextThemesProvider>;
+}