Add ActiveCampaign hosted MCP plugin

[staging-devin-ai-integration]

Summary

Adds ActiveCampaign as a hosted MCP plugin: the official remote server at https://mcp.app-us1.com/http, plus the six Agent Skills ActiveCampaign ships in ActiveCampaign/activecampaign-plugin (contacts, campaigns, automations, deals, deliverability, reporting), copied verbatim.

The endpoint and transport come from the vendor's own mcp.json (streamable-http), and the OAuth path is verified live against the running server rather than assumed:

• initialize → 401 with WWW-Authenticate: Bearer resource_metadata=".../.well-known/oauth-protected-resource"
• AS metadata advertises /oauth/register, authorization_code + refresh_token, PKCE S256, token_endpoint_auth_method: none
• DCR exercised with the exact payload the webapp's register_oauth_client sends, using the default redirect URI ({backend_url}/mcp/oauth/callback) → 201, echoing our redirect URI and issuing a public PKCE client

So no redirect-URI override (LegacyRedirectURIStrategy) is needed on the webapp side. Only the user-consent round trip is untested; that needs a real ActiveCampaign account.

Logo is the official ActiveCampaign GitHub organization avatar, stored locally as plugins/activecampaign/logo.png (Simple Icons has no activecampaign entry).

python3 scripts/validate.py (plus --fix / --fetch): ok: 172 entries (171 authored, 1 upstream).

The webapp-side marketplace listing row landed separately in usacognition/devin-webapp#70474; a follow-up webapp PR bumps MARKETPLACE_COMMIT_SHA and regenerates marketplace_facts.json once this merges.

Link to Devin session: https://staging.itsdev.in/sessions/1d76becc8d0546e490d72be367b903a8
Open in Devin Desktop: https://staging.itsdev.in/desktop/session/1d76becc8d0546e490d72be367b903a8?variant=devin-insiders
Requested by: @mitchell-cog

---

Note

Devin errored when opening this Pull Request as mitchell-cog.
As a fallback, Devin opened this PR as itself.

---

Devin Review

Status	Commit
⚪ Not started	—

Run Devin Review

[staging-devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment, CI, and merge conflict monitoring

---

Original prompt from Mitchell

add activecampaign mcp with patos mcp skill