fix: add @types/jest so ForkTsCheckerWebpackPlugin sees jest globals

The tsconfig declares "types": ["jest"] but @types/jest was not
installed, so TypeScript treated jest as a namespace rather than a
value.  Adding the matching type definitions lets the webpack
type-checker process test files without errors.

Also bump frontend-base to fix the @src alias in jest config.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: arbrandes