docs(user-guide): clarify default integration selection logic

[alezander86]

Summary

Improves documentation clarity around how CodeMie selects a default integration
when none is explicitly chosen by the user.

Changes

• docs/user-guide/tools_integrations/integrations/index.md — rewrote the intro
  to use consistent type names; added How the Default Integration Is Selected
  section with priority table, scenarios, and tips; updated the note to reference
  isAdmin and applications_admin roles explicitly
• docs/user-guide/getting-started/glossary.md — split ### Integration into two
  entries: ### Integration (type definitions) and new ### Default Integration
  (priority table + link to full article)

Testing

• Tested locally with npm start
• All pages render correctly
• Internal links work
• Sidebar navigation works

Quality Checks

• npm run check passes
• No MDX compilation errors
• Commit messages follow Conventional Commits
• No secrets or credentials in documentation

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