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>

skills/analytics-tracking/SKILL.md

@@ -285,6 +285,20 @@ dataLayer.push({
 
 ---
 
+## Tool Integrations
+
+For implementation, see the [tools registry](../../tools/REGISTRY.md). Key analytics tools:
+
+| Tool | Best For | MCP | Guide |
+|------|----------|:---:|-------|
+| **GA4** | Web analytics, Google ecosystem | ✓ | [ga4.md](../../tools/integrations/ga4.md) |
+| **Mixpanel** | Product analytics, event tracking | - | [mixpanel.md](../../tools/integrations/mixpanel.md) |
+| **Amplitude** | Product analytics, cohort analysis | - | [amplitude.md](../../tools/integrations/amplitude.md) |
+| **PostHog** | Open-source analytics, session replay | - | [posthog.md](../../tools/integrations/posthog.md) |
+| **Segment** | Customer data platform, routing | - | [segment.md](../../tools/integrations/segment.md) |
+
+---
+
 ## Related Skills
 
 - **ab-test-setup**: For experiment tracking

skills/email-sequence/SKILL.md

@@ -283,6 +283,20 @@ What to measure and benchmarks
 
 ---
 
+## Tool Integrations
+
+For implementation, see the [tools registry](../../tools/REGISTRY.md). Key email tools:
+
+| Tool | Best For | MCP | Guide |
+|------|----------|:---:|-------|
+| **Customer.io** | Behavior-based automation | - | [customer-io.md](../../tools/integrations/customer-io.md) |
+| **Mailchimp** | SMB email marketing | ✓ | [mailchimp.md](../../tools/integrations/mailchimp.md) |
+| **Resend** | Developer-friendly transactional | ✓ | [resend.md](../../tools/integrations/resend.md) |
+| **SendGrid** | Transactional email at scale | - | [sendgrid.md](../../tools/integrations/sendgrid.md) |
+| **Kit** | Creator/newsletter focused | - | [kit.md](../../tools/integrations/kit.md) |
+
+---
+
 ## Related Skills
 
 - **onboarding-cro**: For in-app onboarding (email supports this)

skills/paid-ads/SKILL.md

@@ -289,6 +289,21 @@ Before launching campaigns, ensure proper tracking and account setup.
 
 ---
 
+## Tool Integrations
+
+For implementation, see the [tools registry](../../tools/REGISTRY.md). Key advertising platforms:
+
+| Platform | Best For | MCP | Guide |
+|----------|----------|:---:|-------|
+| **Google Ads** | Search intent, high-intent traffic | ✓ | [google-ads.md](../../tools/integrations/google-ads.md) |
+| **Meta Ads** | Demand gen, visual products, B2C | - | [meta-ads.md](../../tools/integrations/meta-ads.md) |
+| **LinkedIn Ads** | B2B, job title targeting | - | [linkedin-ads.md](../../tools/integrations/linkedin-ads.md) |
+| **TikTok Ads** | Younger demographics, video | - | [tiktok-ads.md](../../tools/integrations/tiktok-ads.md) |
+
+For tracking, see also: [ga4.md](../../tools/integrations/ga4.md), [segment.md](../../tools/integrations/segment.md)
+
+---
+
 ## Related Skills
 
 - **copywriting**: For landing page copy that converts ad traffic

skills/referral-program/SKILL.md

@@ -231,6 +231,20 @@ They get [their reward] too.
 
 ---
 
+## Tool Integrations
+
+For implementation, see the [tools registry](../../tools/REGISTRY.md). Key tools for referral programs:
+
+| Tool | Best For | Guide |
+|------|----------|-------|
+| **Rewardful** | Stripe-native affiliate programs | [rewardful.md](../../tools/integrations/rewardful.md) |
+| **Tolt** | SaaS affiliate programs | [tolt.md](../../tools/integrations/tolt.md) |
+| **Mention Me** | Enterprise referral programs | [mention-me.md](../../tools/integrations/mention-me.md) |
+| **Dub.co** | Link tracking and attribution | [dub-co.md](../../tools/integrations/dub-co.md) |
+| **Stripe** | Payment processing (for commission tracking) | [stripe.md](../../tools/integrations/stripe.md) |
+
+---
+
 ## Related Skills
 
 - **launch-strategy**: For launching referral program effectively