deps: upgrade TypeScript from v5 to v6

[ericfitz]

Summary

TypeScript 6.0.2 is now available. We are currently on 5.9.3. This is a major version bump that requires ecosystem compatibility validation before upgrading.

Current State

• Installed: 5.9.3
• Latest: 6.0.2
• Release notes: https://devblogs.microsoft.com/typescript/announcing-typescript-6-0/

Prerequisites

• Confirm Angular 21.x officially supports TypeScript 6
• Confirm @angular/compiler-cli compatibility with TS 6
• Check eslint-typescript / angular-eslint compatibility
• Review TS 6 breaking changes against our codebase

Approach

1. Create a feature branch
2. Update typescript to ^6.0.2 in package.json
3. Run pnpm install
4. Fix any build errors from breaking changes
5. Run full test suite
6. Run lint

Notes

Discovered during dependency bump on 2026-03-29. No security implications — this is a planned ecosystem upgrade.