docs(wiki): update documentation for migration system and integration tests

[CalvinAllen]

Description

Update the project wiki to document recent changes to the migration system and integration testing.

Changes to Document

Migration System Refactor (PR #129)

• New plugin-style architecture for migration providers
• internal/migration package with Provider interface and registry
• Migration providers organized by runtime:
  • src/migrations/node/ - nvm, fnm, system
  • src/migrations/python/ - pyenv, system
  • src/migrations/ruby/ - rbenv, rvm, chruby, system, uru
• How to add a new migration provider

uru Support (PR #130)

• Added uru detection for Ruby on Windows/Linux/macOS
• Configuration location: ~/.uru/rubies.json (or URU_HOME env var)
• How uru differs from other version managers (registers existing installs rather than installing)

Integration Tests

• Weekly integration test workflow structure
• Migration test coverage matrix:
  • Node.js: nvm (Ubuntu, Windows), fnm (macOS), system (all platforms)
  • Python: pyenv (Ubuntu, macOS, Windows), system (all platforms)
  • Ruby: rbenv (Ubuntu, macOS), uru (Windows), system (all platforms)
• How to add new integration tests

Acceptance Criteria

• Document the migration provider interface and how to implement it
• List all supported migration providers by runtime
• Explain the integration test structure and how to run them manually
• Add examples for adding new migration providers