feat: locked-feature upgrade prompts route to billing + track upgrade interest (v0.81.0)

UpgradeDialog's CTA now sends users to Settings > Billing (with a feature-specific banner) instead of a generic support-ticket prefill, and fires a best-effort tracking beacon recording which feature triggered the click. New feature_upgrade_clicks table + Admin > Insights chart ("Most-requested locked features") gives admins visibility into which locked features actually drive upgrade interest.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/app/(app)/settings/billing/page.tsx

@@ -8,6 +8,8 @@ import { ManageBillingButton } from "@/components/settings/manage-billing-button
 import { UsageQuotaSection } from "@/components/settings/usage-quota-section";
 import { BillingDetailsForm } from "@/components/settings/billing-details-form";
 import { Badge } from "@/components/ui/badge";
+import { FEATURE_DEFINITIONS } from "@/lib/feature-flags";
+import { Sparkles } from "lucide-react";
 
 export const metadata: Metadata = {};
 
@@ -17,10 +19,11 @@ function describeLimit(n: number, unit: string): string {
   return n === UNLIMITED ? `Unlimited ${unit}` : `${n} ${unit}`;
 }
 
-export default async function BillingPage({ searchParams }: { searchParams: Promise<{ checkout?: string }> }) {
+export default async function BillingPage({ searchParams }: { searchParams: Promise<{ checkout?: string; upgrade?: string }> }) {
   const session = await auth.api.getSession({ headers: await headers() });
   if (!session) return null;
-  const { checkout } = await searchParams;
+  const { checkout, upgrade } = await searchParams;
+  const upgradeFeature = FEATURE_DEFINITIONS.find((f) => f.key === upgrade);
 
   const currentMonth = new Date().toISOString().slice(0, 7);
 
@@ -66,6 +69,14 @@ export default async function BillingPage({ searchParams }: { searchParams: Prom
 
   return (
     <div className="space-y-8">
+      {upgradeFeature && (
+        <div className="flex items-start gap-3 rounded-lg border border-primary/40 bg-primary/5 p-4 text-sm">
+          <Sparkles className="h-4 w-4 text-primary shrink-0 mt-0.5" />
+          <p>
+            Upgrading unlocks <strong>{upgradeFeature.label}</strong> — {upgradeFeature.description}
+          </p>
+        </div>
+      )}
       {checkout === "success" && (
         <div className="rounded-lg border border-primary/40 bg-primary/5 p-4 text-sm">
           Payment received — your plan updates within a few seconds as Stripe confirms it. Refresh if it doesn&apos;t show up right away.