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

lib/db/migrations/0001_even_baron_strucker.sql

@@ -0,0 +1,37 @@
+CREATE TABLE IF NOT EXISTS "Subscription" (
+	"userId" uuid PRIMARY KEY NOT NULL,
+	"tier" varchar DEFAULT 'free' NOT NULL,
+	"status" varchar DEFAULT 'active' NOT NULL,
+	"stripeCustomerId" text,
+	"stripeSubscriptionId" text,
+	"currentPeriodEnd" timestamp,
+	"createdAt" timestamp DEFAULT now() NOT NULL,
+	"updatedAt" timestamp DEFAULT now() NOT NULL
+);
+--> statement-breakpoint
+CREATE TABLE IF NOT EXISTS "Usage" (
+	"userId" uuid NOT NULL,
+	"periodKey" varchar(10) NOT NULL,
+	"messageCount" integer DEFAULT 0 NOT NULL,
+	"toolCallCount" integer DEFAULT 0 NOT NULL,
+	"updatedAt" timestamp DEFAULT now() NOT NULL,
+	CONSTRAINT "Usage_userId_periodKey_pk" PRIMARY KEY("userId","periodKey")
+);
+--> statement-breakpoint
+CREATE TABLE IF NOT EXISTS "WebhookEvent" (
+	"id" text PRIMARY KEY NOT NULL,
+	"type" text NOT NULL,
+	"receivedAt" timestamp DEFAULT now() NOT NULL
+);
+--> statement-breakpoint
+DO $$ BEGIN
+ ALTER TABLE "Subscription" ADD CONSTRAINT "Subscription_userId_User_id_fk" FOREIGN KEY ("userId") REFERENCES "public"."User"("id") ON DELETE no action ON UPDATE no action;
+EXCEPTION
+ WHEN duplicate_object THEN null;
+END $$;
+--> statement-breakpoint
+DO $$ BEGIN
+ ALTER TABLE "Usage" ADD CONSTRAINT "Usage_userId_User_id_fk" FOREIGN KEY ("userId") REFERENCES "public"."User"("id") ON DELETE no action ON UPDATE no action;
+EXCEPTION
+ WHEN duplicate_object THEN null;
+END $$;