Finish Slack custom MCP settings and compatible beta dependency updates

[makeitfutureDev]

Slack Settings now supports adding, updating and removing channel and personal Custom MCP connections. Blank tokens retain existing credentials; delayed requests recheck permission before saving, and repeated saves reuse the parent view to avoid exhausting Slack’s modal stack.

Also ports the compatible Express, Acorn and Composio SDK dependency updates to beta, tests the real SDK transport, and accepts legal download filename header representations. Existing beta CLI and documentation changes are preserved. File-staging instructions explicitly map server identities to the accepted user/agent argument values after live explanation QA exposed ambiguous wording.

Validation:

• Full regression/coverage: 3,770 passed, zero failures, 32 opt-in live skips. Coverage 94.39% lines, 86.19% branches, 90.06% functions.
• Static checks, secret scan, security coverage, production dependency audit and DCO passed; zero vulnerabilities.
• Dependency regressions on Node 22.13 and Node 24; independent Slack review with 94 focused tests passed.
• Clarified staging mapping: 29 focused tests passed and independent 20-test review passed. Original live explanation failures remain recorded; deployed retest pending.
• Seven exact Custom MCP live case definitions registered and reread in the private QA registry. Native client and authenticated admin acceptance remain pending access; mock tests are not recorded as live passes.

Published Composio SDK engine requirements exceed the project minimum in both the previous and updated versions. Exercised paths pass on Node 22.13; the project minimum is unchanged, without claiming upstream support for that Node version.

Scope: beta only. Teams, VPN expansion, WhatsApp and cross-agent work are excluded.