chore: reference AIContextItem types from LS, remove duplicate types

Description

This change is split out from feat: enable duo chat dependencies context cate... (!2099 - merged)

Instead of redeclaring the AIContextItem structure within VSCode, we now reference the types from the language server, as the single source of truth.

This ensures the types used in VSCode stay up to date, and means one less place we need to manually add new categories.

Related Issues

Resolves #1666 (closed)

How has this been tested?

• code compiles
• smoke test

(no functional changes expected)

Screenshots (if appropriate)

What CHANGELOG entry will this MR create?

• fix: Bug fix fixes - a user-facing issue in production - included in changelog
• feature: New feature - a user-facing change which adds functionality - included in changelog
• BREAKING CHANGE: (fix or feature that would cause existing functionality to change) - should bump major version, mentioned in the changelog
• None - other non-user-facing changes