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/sendgrid.md

@@ -0,0 +1,161 @@
+# SendGrid
+
+Email delivery platform for transactional and marketing emails.
+
+## Capabilities
+
+| Integration | Available | Notes |
+|-------------|-----------|-------|
+| API | ✓ | Mail Send API, Marketing API |
+| MCP | - | Not available |
+| CLI | - | Not available |
+| SDK | ✓ | Official libraries for most languages |
+
+## Authentication
+
+- **Type**: API Key
+- **Header**: `Authorization: Bearer {api_key}`
+- **Get key**: Settings > API Keys in SendGrid dashboard
+
+## Common Agent Operations
+
+### Send email
+
+```bash
+POST https://api.sendgrid.com/v3/mail/send
+
+Authorization: Bearer {api_key}
+
+{
+  "personalizations": [{
+    "to": [{"email": "user@example.com"}]
+  }],
+  "from": {"email": "hello@example.com"},
+  "subject": "Welcome!",
+  "content": [{
+    "type": "text/html",
+    "value": "<h1>Welcome!</h1>"
+  }]
+}
+```
+
+### Send with template
+
+```bash
+POST https://api.sendgrid.com/v3/mail/send
+
+{
+  "personalizations": [{
+    "to": [{"email": "user@example.com"}],
+    "dynamic_template_data": {
+      "name": "John",
+      "order_id": "12345"
+    }
+  }],
+  "from": {"email": "hello@example.com"},
+  "template_id": "d-xxx"
+}
+```
+
+### Add contact to list
+
+```bash
+PUT https://api.sendgrid.com/v3/marketing/contacts
+
+{
+  "list_ids": ["list-id"],
+  "contacts": [{
+    "email": "user@example.com",
+    "first_name": "John",
+    "last_name": "Doe"
+  }]
+}
+```
+
+### Search contacts
+
+```bash
+POST https://api.sendgrid.com/v3/marketing/contacts/search
+
+{
+  "query": "email LIKE 'user@%'"
+}
+```
+
+### Get email statistics
+
+```bash
+GET https://api.sendgrid.com/v3/stats?start_date=2024-01-01&end_date=2024-01-31
+
+Authorization: Bearer {api_key}
+```
+
+### Get bounces
+
+```bash
+GET https://api.sendgrid.com/v3/suppression/bounces
+
+Authorization: Bearer {api_key}
+```
+
+### Get spam reports
+
+```bash
+GET https://api.sendgrid.com/v3/suppression/spam_reports
+
+Authorization: Bearer {api_key}
+```
+
+### Validate email
+
+```bash
+POST https://api.sendgrid.com/v3/validations/email
+
+{
+  "email": "user@example.com"
+}
+```
+
+## Webhook Events
+
+| Event | Description |
+|-------|-------------|
+| `processed` | Email accepted |
+| `delivered` | Email delivered |
+| `open` | Email opened |
+| `click` | Link clicked |
+| `bounce` | Hard/soft bounce |
+| `dropped` | Email dropped |
+| `spamreport` | Marked as spam |
+| `unsubscribe` | Unsubscribed |
+
+## Node.js SDK
+
+```javascript
+const sgMail = require('@sendgrid/mail');
+sgMail.setApiKey('SG.xxx');
+
+await sgMail.send({
+  to: 'user@example.com',
+  from: 'hello@example.com',
+  subject: 'Welcome!',
+  html: '<h1>Welcome!</h1>'
+});
+```
+
+## When to Use
+
+- Transactional email at scale
+- Marketing email campaigns
+- Email validation
+- Deliverability management
+
+## Rate Limits
+
+- Free: 100 emails/day
+- Paid: Varies by plan (up to millions/month)
+
+## Relevant Skills
+
+- email-sequence
+- analytics-tracking