added cognito-to-descope migration skill

[mrunankpawar]

Description

This skill will be helpful for customers and prospects to help/guide them migrate from Cognito to Descope with any agent of their choice.

[shuni-bot-dev]

🐕 Review complete — View session on Shuni Portal 🐾

[shuni-bot-dev]

🐕 Shuni's Review

Adds a new cognito-to-descope migration skill (~2,800 lines of guidance + reference docs).

Sniffed out 4 issues:

• 1 🟠 HIGH: plugin.json version not bumped per CLAUDE.md (new skill = minor bump → 1.2.0)
• 3 🟡 MEDIUM: incorrect Node SDK method name (management.user.logout doesn't exist), wrong Python kwarg (logout_user(user_id=...) will TypeError), JWT payload decoded with 'base64' instead of 'base64url'

The 🟠 HIGH is a clear project-rule violation. The 🟡 MEDIUMs in IMPLEMENTATION-NOTES-DIST.md will lead users to write code that doesn't run — worth fixing before this lands so it can't propagate into customer migrations. Needs a bath!

Note on plugin.json: per CLAUDE.md, every PR must bump .claude-plugin/plugin.json. A new skill is a minor bump. Current version on this branch is still 1.1.1 (same as main); it should be 1.2.0.