feat: add marketing tools registry for agent discovery

Create centralized tools/ directory with REGISTRY.md index and 29
integration guides covering analytics, SEO, CRM, payments, referral,
email, ads, automation, and commerce platforms.

Each guide includes API endpoints, authentication, common operations,
and links to relevant skills. Updated AGENTS.md and key skills
(referral-program, analytics-tracking, email-sequence, paid-ads)
with tool integration references.

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

tools/integrations/stripe.md

@@ -0,0 +1,148 @@
+# Stripe
+
+Payment processing, subscriptions, and billing for internet businesses.
+
+## Capabilities
+
+| Integration | Available | Notes |
+|-------------|-----------|-------|
+| API | ✓ | Comprehensive REST API |
+| MCP | ✓ | Available via Stripe MCP server |
+| CLI | ✓ | `stripe` CLI for testing and webhooks |
+| SDK | ✓ | Official SDKs for most languages |
+
+## Authentication
+
+- **Type**: API Key
+- **Header**: `Authorization: Bearer sk_live_xxx` or `sk_test_xxx`
+- **Keys**: Secret key (server), Publishable key (client)
+
+## Common Agent Operations
+
+### List customers
+
+```bash
+GET https://api.stripe.com/v1/customers?limit=10
+```
+
+### Get customer by email
+
+```bash
+GET https://api.stripe.com/v1/customers?email=user@example.com
+```
+
+### Get subscription
+
+```bash
+GET https://api.stripe.com/v1/subscriptions/{subscription_id}
+```
+
+### List subscriptions for customer
+
+```bash
+GET https://api.stripe.com/v1/subscriptions?customer={customer_id}
+```
+
+### Create checkout session
+
+```bash
+POST https://api.stripe.com/v1/checkout/sessions
+
+customer={customer_id}
+&line_items[0][price]={price_id}
+&line_items[0][quantity]=1
+&mode=subscription
+&success_url=https://example.com/success
+&cancel_url=https://example.com/cancel
+```
+
+### Create customer portal session
+
+```bash
+POST https://api.stripe.com/v1/billing_portal/sessions
+
+customer={customer_id}
+&return_url=https://example.com/account
+```
+
+### List recent invoices
+
+```bash
+GET https://api.stripe.com/v1/invoices?customer={customer_id}&limit=10
+```
+
+### Get payment intent
+
+```bash
+GET https://api.stripe.com/v1/payment_intents/{payment_intent_id}
+```
+
+## Webhook Events
+
+Key events to handle:
+
+| Event | When | Action |
+|-------|------|--------|
+| `checkout.session.completed` | Successful checkout | Provision access |
+| `customer.subscription.created` | New subscription | Update user record |
+| `customer.subscription.updated` | Plan change | Update entitlements |
+| `customer.subscription.deleted` | Cancellation | Revoke access |
+| `invoice.payment_failed` | Payment failed | Notify user, retry |
+| `invoice.paid` | Invoice paid | Confirm payment |
+
+### Verify webhook signature
+
+```javascript
+const event = stripe.webhooks.constructEvent(
+  payload,
+  sig,
+  webhookSecret
+);
+```
+
+## CLI Commands
+
+```bash
+# Listen to webhooks locally
+stripe listen --forward-to localhost:3000/webhooks
+
+# Trigger test events
+stripe trigger checkout.session.completed
+
+# List recent events
+stripe events list --limit 10
+
+# Get resource
+stripe customers retrieve cus_xxx
+```
+
+## Key Objects
+
+- **Customer** - User billing profile
+- **Subscription** - Recurring billing
+- **Price** - Pricing configuration
+- **Product** - What you sell
+- **Invoice** - Billing document
+- **PaymentIntent** - One-time payment
+- **Checkout Session** - Hosted payment page
+
+## When to Use
+
+- Processing payments
+- Managing subscriptions
+- Creating checkout flows
+- Handling billing portal
+- Querying customer data
+- Revenue analytics
+
+## Rate Limits
+
+- 100 read requests per second
+- 100 write requests per second
+- Higher limits available on request
+
+## Relevant Skills
+
+- pricing-strategy
+- referral-program (Stripe-integrated affiliate tools)
+- analytics-tracking (revenue tracking)