feat: add is_mcp_enabled setting to app manifest

[mwbrooks]

Changelog

Add support for the settings.is_mcp_enabled: <bool> manifest property to enable or disable the Slack MCP Server.

Summary

This pull request adds the settings.is_mcp_enabled boolean field to the AppSettings manifest type. When omitted, the backend defaults to false.

Testing

# Create a new Agent app
$ lack create agent

# Update the manifest.json with `settings.is_mcp_enabled: true`
$ vim manifest.json
# → Add `settings.is_mcp_enabled: true`

# Install the app
$ lack run
# → CTRL+C

# Confirm the MCP is enabled
$ lack app settings
# → Select "AI & Agents" on left-nav
# → Scroll to bottom and confirm MCP is enabled

Notes

Follows the existing *bool + omitempty pattern used by other boolean settings (socket_mode_enabled, org_deploy_enabled, token_rotation_enabled).

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.26%. Comparing base (d2ab928) to head (48c0231).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #513   +/-   ##
=======================================
  Coverage   71.26%   71.26%           
=======================================
  Files         222      222           
  Lines       18682    18682           
=======================================
  Hits        13314    13314           
- Misses       4187     4189    +2     
+ Partials     1181     1179    -2     

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[zimeg]

@mwbrooks So nice! 💃 🤖 🕺 🪩 ✨

[mwbrooks]

Thanks a bunch @zimeg! 🙇🏻