fix: language default, google OAuth cookie issue, add admin tier/usage controls

- ai-generate-dialog: useLocale() returns {locale,setLocale} object, not
  string — was stringifying whole object as default language value
- auth/server: add trustedOrigins so session cookie survives reverse-proxy
  deployments where BETTER_AUTH_URL differs from container's own view
- admin: add tier limit editor (/admin/tiers) and per-user usage reset
  button, both audit-logged

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/app/admin/layout.tsx

@@ -3,13 +3,14 @@ import { headers } from "next/headers";
 import { auth } from "@/lib/auth/server";
 import { db, users, eq } from "@epicure/db";
 import Link from "next/link";
-import { Shield, Users, BookOpen, Settings, BarChart3, ClipboardList, HardDrive, Bot, ArrowLeft } from "lucide-react";
+import { Shield, Users, BookOpen, Settings, BarChart3, ClipboardList, HardDrive, Bot, ArrowLeft, Gauge } from "lucide-react";
 import { cn } from "@/lib/utils";
 
 const adminNav = [
   { href: "/admin", label: "Overview", icon: BarChart3 },
   { href: "/admin/users", label: "Users", icon: Users },
   { href: "/admin/recipes", label: "Recipes", icon: BookOpen },
+  { href: "/admin/tiers", label: "Tier Limits", icon: Gauge },
   { href: "/admin/audit-logs", label: "Audit Logs", icon: ClipboardList },
   { href: "/admin/storage", label: "Storage", icon: HardDrive },
   { href: "/admin/ai-config", label: "AI Config", icon: Bot },