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/api/v1/admin/users/[id]/usage/route.ts

@@ -0,0 +1,39 @@
+import { NextRequest, NextResponse } from "next/server";
+import { requireAdmin } from "@/lib/api-auth";
+import { db, userUsage, auditLogs, eq, and } from "@epicure/db";
+import { randomUUID } from "crypto";
+
+interface RouteContext {
+  params: Promise<{ id: string }>;
+}
+
+function currentMonth() {
+  const now = new Date();
+  return `${now.getFullYear()}-${String(now.getMonth() + 1).padStart(2, "0")}`;
+}
+
+export async function PATCH(req: NextRequest, { params }: RouteContext) {
+  const { session, response } = await requireAdmin();
+  if (response) return response;
+
+  const { id } = await params;
+  const month = currentMonth();
+
+  const [updated] = await db
+    .update(userUsage)
+    .set({ aiCallsUsed: 0, recipeCount: 0, storageUsedMb: 0 })
+    .where(and(eq(userUsage.userId, id), eq(userUsage.month, month)))
+    .returning();
+
+  await db.insert(auditLogs).values({
+    id: randomUUID(),
+    userId: session!.user.id,
+    action: "admin.user.reset_usage",
+    targetType: "user",
+    targetId: id,
+    metadata: JSON.stringify({ month }),
+    createdAt: new Date(),
+  });
+
+  return NextResponse.json({ usage: updated ?? { userId: id, month, aiCallsUsed: 0, recipeCount: 0, storageUsedMb: 0 } });
+}