Initial import: property management SaaS + security hardening + admin dashboard

Property Management Network — Next.js 16 (App Router), Better Auth,
Drizzle ORM over PostgreSQL, Stripe, OpenAI, Resend.

Includes:
- Security hardening: access-control/IDOR fixes, TLS-by-default DB layer,
  constant-time cron auth, strict security headers, atomic AI quota gating,
  HTML/email output encoding, demo-backdoor disabled in production.
- Superadmin dashboard at /admin (overview/MRR, server-paginated users with
  ban/impersonate/plan/delete, billing, platform activity + admin audit log,
  AI usage, system health) via the Better Auth admin plugin.
- Seed/migration utility scripts under scripts/.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/api/stripe/checkout/route.ts

@@ -0,0 +1,61 @@
+import { NextResponse } from "next/server"
+import { eq } from "drizzle-orm"
+import { db } from "@/lib/db"
+import { profiles } from "@/lib/db/schema"
+import { getSessionUser } from "@/lib/session"
+import { stripe } from "@/lib/stripe/client"
+import { PLAN_PRICES } from "@/lib/stripe/plans"
+
+export async function POST(request: Request) {
+  const user = await getSessionUser()
+  if (!user) return NextResponse.json({ error: "Unauthorized" }, { status: 401 })
+
+  const { plan } = await request.json() as { plan: string }
+
+  const planConfig = PLAN_PRICES[plan]
+  if (!planConfig) return NextResponse.json({ error: "Invalid plan" }, { status: 400 })
+
+  const profile = await db.query.profiles.findFirst({
+    where: eq(profiles.id, user.id),
+    columns: { stripe_customer_id: true, email: true, full_name: true },
+  })
+
+  // Get or create Stripe customer
+  let customerId = profile?.stripe_customer_id
+
+  if (!customerId) {
+    const customer = await stripe.customers.create({
+      email: profile?.email ?? user.email,
+      name: profile?.full_name ?? undefined,
+      metadata: { supabase_user_id: user.id },
+    })
+    customerId = customer.id
+
+    await db
+      .update(profiles)
+      .set({ stripe_customer_id: customerId })
+      .where(eq(profiles.id, user.id))
+  }
+
+  const isLifetime = planConfig.interval === "one_time"
+  const appUrl = process.env.NEXT_PUBLIC_APP_URL!
+
+  const session = await stripe.checkout.sessions.create({
+    customer: customerId,
+    mode: isLifetime ? "payment" : "subscription",
+    line_items: [{ price: planConfig.priceId, quantity: 1 }],
+    success_url: `${appUrl}/settings/billing?success=true`,
+    cancel_url: `${appUrl}/settings/billing?canceled=true`,
+    metadata: {
+      supabase_user_id: user.id,
+      plan: planConfig.plan,
+    },
+    ...(isLifetime ? {} : {
+      subscription_data: {
+        metadata: { supabase_user_id: user.id, plan: planConfig.plan },
+      },
+    }),
+  })
+
+  return NextResponse.json({ url: session.url })
+}