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/components/ui/theme-toggle.tsx

@@ -0,0 +1,43 @@
+"use client";
+
+import * as React from "react";
+import { Moon, Sun } from "lucide-react";
+import { useTheme } from "next-themes";
+import { Button } from "@/components/ui/button";
+import { cn } from "@/lib/utils";
+
+type ThemeToggleProps = {
+  className?: string;
+};
+
+export function ThemeToggle({ className }: ThemeToggleProps) {
+  const { theme, setTheme, resolvedTheme } = useTheme();
+  const [mounted, setMounted] = React.useState(false);
+
+  React.useEffect(() => {
+    setMounted(true);
+  }, []);
+
+  const isDark = mounted && (resolvedTheme === "dark" || theme === "dark");
+
+  return (
+    <Button
+      type="button"
+      variant="ghost"
+      size="icon"
+      className={cn("size-9 shrink-0 text-foreground", className)}
+      aria-label={isDark ? "Passer en mode clair" : "Passer en mode sombre"}
+      onClick={() => setTheme(isDark ? "light" : "dark")}
+    >
+      {mounted ? (
+        isDark ? (
+          <Sun className="size-4" aria-hidden />
+        ) : (
+          <Moon className="size-4" aria-hidden />
+        )
+      ) : (
+        <span className="size-4 inline-block" aria-hidden />
+      )}
+    </Button>
+  );
+}