#13511: feat: Short menu for testing model selection

## Summary Implements a short menu option for testing model selection to keep the UI focused during development/testing. ## Changes - Added environment-based menu configuration to navigation.ts - Updated app-render.ts to use short menu when VITE_TEST_MODE is enabled - Added vite-env.d.ts for proper TypeScript support of import.meta.env ## Testing - Verified app-render.ts implementation meets all acceptance criteria - Menu correctly switches between full and short configuration based on environment ## Related - US-001: Environment-based menu configuration - US-002: Short menu in test mode <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR introduces a “short menu” navigation configuration intended to simplify the UI during testing. It adds `SHORT_TAB_GROUPS` and env-based helpers in `ui/src/ui/navigation.ts`, updates `ui/src/ui/app-render.ts` to select between full vs short tab groups, and adds TypeScript env typings in `ui/src/vite-env.d.ts`, along with new/updated Vitest coverage around these helpers. Main integration point is the sidebar tab rendering in `renderApp`, which now maps over a `tabGroups` selection rather than always using `TAB_GROUPS`. <h3>Confidence Score: 3/5</h3> - Mostly safe to merge, but there are a couple of correctness/repo-hygiene issues to address first. - The navigation refactor is straightforward, but the env flag used in code (`VITE_SHORT_MENU`) appears to conflict with the PR’s stated `VITE_TEST_MODE` behavior, and the PR adds an apparent stray progress file to the repo. - ui/src/ui/app-render.ts, progress.txt <!-- greptile_other_comments_section --> <!-- /greptile_comment -->