[Refactor] [Studio]: remove proxy stubs and relocate dashboard modals

[Gautam25Raj]

Summary

Cleans up redundant export shims and relocates modals inside apps/studio/components/dashboard into dedicated submodules.

Details

1. Delete Proxy Stubs:
   • Removed AccountMenu.tsx, AccountMenuItem.tsx, AccountMenuTheme.tsx, and StudioNavigation.tsx from the dashboard root.
2. Relocate Modals:
   • Moved WorkspaceSearchModal.tsx, NewDocumentModal.tsx, and ImportProfileModal.tsx into apps/studio/components/dashboard/modals/.
3. Import Updates:
   • Updated DashboardModalsHost.tsx to dynamically load modals from ./.
   • Updated StudioSidebar.tsx and MobileHeader.tsx to import NewDocumentButton from ../modals/NewDocumentModal.
   • Updated index.ts to export modals from ./modals/....

Verification

• vitest run in @veriworkly/studio: 23 test files passed (236 tests).
• Prettier: verified zero style differences across dashboard components.
• ESLint: 0 errors.
• next build: completed successfully.