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/tiers/page.tsx

@@ -0,0 +1,24 @@
+import type { Metadata } from "next";
+import { db, tierDefinitions } from "@epicure/db";
+import { TierLimitsForm } from "@/components/admin/tier-limits-form";
+
+export const metadata: Metadata = { title: "Tier Limits – Admin" };
+
+export default async function AdminTiersPage() {
+  const tiers = await db.select().from(tierDefinitions);
+
+  return (
+    <div className="space-y-8">
+      <div>
+        <h1 className="text-2xl font-bold tracking-tight">Tier Limits</h1>
+        <p className="text-muted-foreground text-sm mt-1">
+          Change monthly quotas per tier. Takes effect immediately for all users on that tier.
+        </p>
+      </div>
+
+      {tiers.map((tierDefinition) => (
+        <TierLimitsForm key={tierDefinition.tier} tierDefinition={tierDefinition} />
+      ))}
+    </div>
+  );
+}