Add Stripe subscription system and n8n chat webhook

- Add Stripe SDK and subscription management
- Create checkout, webhook, and portal API routes
- Add pricing page with plan cards
- Create subscriptions table in Supabase
- Update database types for subscriptions
- Configure n8n webhook for AI chat responses

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/app/api/stripe/portal/route.ts

@@ -0,0 +1,38 @@
+import { NextResponse } from 'next/server'
+import { createClient } from '@/lib/supabase/server'
+import { stripe } from '@/lib/stripe/config'
+import type { Database } from '@/types/database'
+
+type Subscription = Database['public']['Tables']['subscriptions']['Row']
+
+export async function POST() {
+  try {
+    const supabase = await createClient()
+    const { data: { user } } = await supabase.auth.getUser()
+
+    if (!user) {
+      return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
+    }
+
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const { data: subscription } = await (supabase as any)
+      .from('subscriptions')
+      .select('stripe_customer_id')
+      .eq('user_id', user.id)
+      .single() as { data: Pick<Subscription, 'stripe_customer_id'> | null }
+
+    if (!subscription?.stripe_customer_id) {
+      return NextResponse.json({ error: 'No subscription found' }, { status: 404 })
+    }
+
+    const session = await stripe.billingPortal.sessions.create({
+      customer: subscription.stripe_customer_id,
+      return_url: `${process.env.NEXT_PUBLIC_SITE_URL}/dashboard/settings`,
+    })
+
+    return NextResponse.json({ url: session.url })
+  } catch (error) {
+    console.error('Portal error:', error)
+    return NextResponse.json({ error: 'Failed to create portal session' }, { status: 500 })
+  }
+}