feat: add Composio as integration layer for OAuth-heavy marketing tools

Adds Composio MCP server as an alternative integration method for tools
lacking native MCP support (HubSpot, Salesforce, Meta Ads, LinkedIn Ads,
Google Sheets, Slack, Notion, etc.). Existing CLIs and MCP servers are
unchanged — Composio is additive only.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tools/REGISTRY.md

@@ -85,6 +85,7 @@ Quick reference for AI agents to discover tool capabilities and integration meth
 | sanity | Headless CMS | ✓ | - | ✓ | ✓ | [sanity.md](integrations/sanity.md) |
 | contentful | Headless CMS | ✓ | - | ✓ | ✓ | [contentful.md](integrations/contentful.md) |
 | strapi | Headless CMS | ✓ | - | ✓ | ✓ | [strapi.md](integrations/strapi.md) |
+| composio | Integration Layer | ✓ | ✓ | ✓ | ✓ | [composio.md](integrations/composio.md) |
 
 ---
 
@@ -428,6 +429,16 @@ These tools have Model Context Protocol servers available, enabling direct agent
 
 To use MCP tools, ensure the appropriate MCP server is configured in your environment.
 
+### Composio Integration
+
+[Composio](integrations/composio.md) provides managed OAuth and pre-built connectors for 500+ tools via a single MCP server. It adds MCP access to tools that don't have native MCP servers, including HubSpot, Salesforce, Meta Ads, LinkedIn Ads, Google Sheets, Slack, Notion, and more.
+
+- **Setup**: `npx @composio/mcp@latest setup`
+- **Quick start**: See [tools/composio/README.md](composio/README.md)
+- **Marketing tool mapping**: See [tools/composio/marketing-tools.md](composio/marketing-tools.md)
+
+Use Composio when you need MCP access to OAuth-heavy tools. Prefer native MCP servers (GA4, Stripe, Mailchimp, etc.) when available — they have deeper coverage.
+
 ---
 
 ## Quick Start by Use Case