Add Umami analytics, subscription tiers, tool-call metering

- Analytics: <Analytics /> in root layout loads umami when NEXT_PUBLIC_UMAMI_* env are set
- Subscription: free/pro tiers in Postgres, daily quotas (10msg/5tool free, 1000/500 pro)
- Chat route: checkAndConsume(chat_message) gate before streamText, 429 when exhausted
- Tool metering: getWeather wrapped with withLimit decorator that deducts tool_call quota
- Pricing page at /pricing with upgrade button
- /api/billing/checkout posts to EGBE payment gateway, /api/billing/webhook verifies HMAC and upgrades user on checkout.session.completed
- UsageBadge in chat header polls /api/usage every 15s
- Dropped now-unused entitlements.ts

components/pricing-client.tsx

@@ -0,0 +1,48 @@
+"use client";
+
+import { useState } from "react";
+import { toast } from "sonner";
+import { Button } from "@/components/ui/button";
+import type { Tier } from "@/lib/subscription/config";
+
+export function PricingClient({ currentTier }: { currentTier: Tier }) {
+  const [loading, setLoading] = useState(false);
+
+  if (currentTier === "pro") {
+    return (
+      <p className="text-muted-foreground text-sm">
+        You're on Pro. Manage your subscription through the receipt email link.
+      </p>
+    );
+  }
+
+  const upgrade = async () => {
+    setLoading(true);
+    try {
+      const response = await fetch("/api/billing/checkout", { method: "POST" });
+      const data = await response.json();
+      if (response.ok && data.url) {
+        window.location.href = data.url;
+        return;
+      }
+      toast.error(data.message ?? "Failed to start checkout");
+    } catch (error) {
+      toast.error(error instanceof Error ? error.message : "Checkout failed");
+    } finally {
+      setLoading(false);
+    }
+  };
+
+  return (
+    <div className="flex justify-center">
+      <Button
+        className="px-6"
+        disabled={loading}
+        onClick={upgrade}
+        size="lg"
+      >
+        {loading ? "Opening checkout..." : "Upgrade to Pro"}
+      </Button>
+    </div>
+  );
+}