build: upgrade to TypeScript 6.0 and fix CI ignoreDeprecations

- Bump typescript from ^5.8.3 to ^6.0.0 (resolves to 6.0.3)
- Bump @typescript-eslint/* and typescript-eslint from ^8.34.0 to ^8.58.0
  (minimum version that adds TypeScript 6 peer dep support)
- Set ignoreDeprecations to "6.0" in tsconfig.json to suppress TS 6
  deprecations (target: es5, moduleResolution: node)
- Add highlight.js to webpack CSS loader include paths in both prod and
  dev configs — @patternfly/chatbot imports highlight.js CSS which was
  not covered by the existing include list, causing a webpack error that
  was previously masked by the failing TypeScript step

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: matthewcarleton