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/mailchimp.md

@@ -0,0 +1,150 @@
+# Mailchimp
+
+Email marketing platform for campaigns, automation, and audience management.
+
+## Capabilities
+
+| Integration | Available | Notes |
+|-------------|-----------|-------|
+| API | ✓ | Marketing API for campaigns, audiences, automation |
+| MCP | ✓ | Available via Mailchimp MCP server |
+| CLI | - | Not available |
+| SDK | ✓ | Official SDKs for multiple languages |
+
+## Authentication
+
+- **Type**: API Key or OAuth 2.0
+- **Header**: `Authorization: Bearer {api_key}` or `Authorization: apikey {api_key}`
+- **Base URL**: `https://{dc}.api.mailchimp.com/3.0/` (dc = datacenter from API key)
+
+## Common Agent Operations
+
+### List audiences (lists)
+
+```bash
+GET https://{dc}.api.mailchimp.com/3.0/lists
+```
+
+### Get audience members
+
+```bash
+GET https://{dc}.api.mailchimp.com/3.0/lists/{list_id}/members?count=100
+```
+
+### Add subscriber
+
+```bash
+POST https://{dc}.api.mailchimp.com/3.0/lists/{list_id}/members
+
+{
+  "email_address": "user@example.com",
+  "status": "subscribed",
+  "merge_fields": {
+    "FNAME": "John",
+    "LNAME": "Doe"
+  }
+}
+```
+
+### Update subscriber
+
+```bash
+PATCH https://{dc}.api.mailchimp.com/3.0/lists/{list_id}/members/{subscriber_hash}
+
+{
+  "merge_fields": {
+    "FNAME": "Jane"
+  },
+  "tags": ["customer", "premium"]
+}
+```
+
+### Get campaigns
+
+```bash
+GET https://{dc}.api.mailchimp.com/3.0/campaigns?count=20
+```
+
+### Get campaign report
+
+```bash
+GET https://{dc}.api.mailchimp.com/3.0/reports/{campaign_id}
+```
+
+### Create campaign
+
+```bash
+POST https://{dc}.api.mailchimp.com/3.0/campaigns
+
+{
+  "type": "regular",
+  "recipients": {
+    "list_id": "{list_id}"
+  },
+  "settings": {
+    "subject_line": "Your Subject",
+    "from_name": "Your Name",
+    "reply_to": "reply@example.com"
+  }
+}
+```
+
+### Send campaign
+
+```bash
+POST https://{dc}.api.mailchimp.com/3.0/campaigns/{campaign_id}/actions/send
+```
+
+### List automations
+
+```bash
+GET https://{dc}.api.mailchimp.com/3.0/automations
+```
+
+## Key Metrics
+
+### Campaign Report Fields
+- `emails_sent` - Total sent
+- `opens` - Open count
+- `unique_opens` - Unique opens
+- `open_rate` - Open rate
+- `clicks` - Click count
+- `click_rate` - Click rate
+- `unsubscribes` - Unsubscribe count
+- `bounces` - Bounce count
+
+### Subscriber Hash
+
+Calculate subscriber hash for updates:
+```javascript
+const hash = md5(email.toLowerCase());
+```
+
+## Subscriber Statuses
+
+- `subscribed` - Active subscriber
+- `unsubscribed` - Unsubscribed
+- `cleaned` - Hard bounce
+- `pending` - Awaiting confirmation
+- `transactional` - Transactional only
+
+## When to Use
+
+- Managing email lists and subscribers
+- Creating and sending email campaigns
+- Setting up email automation
+- Analyzing campaign performance
+- Segmenting audiences
+- A/B testing emails
+
+## Rate Limits
+
+- 10 concurrent connections
+- 10 requests per second
+- Batch endpoints for bulk operations
+
+## Relevant Skills
+
+- email-sequence
+- analytics-tracking
+- referral-program