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/users/[id]/page.tsx

@@ -6,6 +6,7 @@ import { Badge } from "@/components/ui/badge";
 import { Card, CardContent, CardHeader, CardTitle } from "@/components/ui/card";
 import { Separator } from "@/components/ui/separator";
 import { UserEditor } from "@/components/admin/user-editor";
+import { ResetUsageButton } from "@/components/admin/reset-usage-button";
 import Link from "next/link";
 import { ArrowLeft } from "lucide-react";
 
@@ -118,6 +119,9 @@ export default async function AdminUserDetailPage({ params }: PageProps) {
               <span className="text-muted-foreground">Storage Used</span>
               <span className="font-medium">{usage?.storageUsedMb ?? 0} MB</span>
             </div>
+            <div className="pt-2">
+              <ResetUsageButton userId={user.id} />
+            </div>
           </CardContent>
         </Card>
       </div>