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/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