fix(navigation): scope the mobile Files tab to the assistant workspace - #393

Summary

On the assistant route, the mobile Files tab opened the global workspace-root browser (every repo) instead of the assistant workspace.

• On /assistant the tab bar treated only repo routes as scoped, so Files called open('files') and rendered the workspace root rather than the assistant directory.
• The Files tab now treats the assistant route as scoped and opens the same dialog=files browser the assistant route already renders, matching the desktop sidebar and the More drawer.
• Repo and global routes are unchanged: repo detail still opens its repo-scoped browser, and / and /schedules still open the workspace root.

Type of Change

• Bug fix
• New feature
• Refactor
• Documentation

Checklist

• Code follows project style (no comments, named imports)
• TypeScript types are properly defined
• Tests added/updated (80% coverage target)
• pnpm lint passes locally
• pnpm typecheck passes locally

Frontend typecheck is clean and eslint reports no errors on the frontend (one pre-existing warning in ChangesWalkthroughDialog.tsx). Navigation tests pass (135 tests), including new cases asserting the assistant route opens dialog=files and / opens the global mobileTab=files. Verified in the running app at a 390px viewport: Files now opens the assistant workspace; / still opens the workspace root.

Summary by CodeRabbit

• Bug Fixes
  • On assistant routes, selecting the Files tab now opens the repository Files dialog. On other routes, it continues to open the Files sheet.