chore: modernize prod server integration tests

[WilliamBergamin]

Summary

• Migrate test framework from Mocha/Chai to Node.js built-in test runner (node:test + node:assert/strict)
• Convert to ESM ("type": "module") and remove legacy dependencies (winston, chai, mocha)
• Use file: references to local @slack/web-api and @slack/socket-mode packages instead of shell-based linking scripts
• Add comprehensive documentation: .env.sample, app manifest.json with setup instructions, and an expanded README
• Add a custom logger utility to replace winston

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.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 520effd

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.52%. Comparing base (3411de3) to head (520effd).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2590   +/-   ##
=======================================
  Coverage   87.52%   87.52%           
=======================================
  Files          62       62           
  Lines       10228    10228           
  Branches      418      418           
=======================================
  Hits         8952     8952           
  Misses       1254     1254           
  Partials       22       22           

Flag	Coverage Δ
cli-hooks	87.52% <ø> (ø)
cli-test	87.52% <ø> (ø)
logger	87.52% <ø> (ø)
oauth	87.52% <ø> (ø)
socket-mode	87.52% <ø> (ø)
web-api	87.52% <ø> (ø)
webhook	87.52% <ø> (ø)

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[zimeg]

@WilliamBergamin It's nice when things get better this is nice! 🧪 ✨