Replace per-page AdminShell wrapping with a single SolidStart layout file
(src/routes/admin.tsx) so the shell mounts once and persists across all
/admin/* navigation — eliminating the sidebar bounce and session re-check
flash that occurred on every page transition.
- Create src/routes/admin.tsx as layout with <Outlet /> for child routes
- Remove <AdminShell> import/wrapper from all 66 route files and 2 shared
components (RoleUserManagementTablePage, UserListPage)
- Fix company.tsx: wrong fetch URL /api/admin/companies → /api/gateway/api/admin/companies
- Add missing auth headers (Authorization Bearer) to company.tsx and users.tsx
- Fix admin/index.tsx API constant from hardcoded localhost:8000 → /api/gateway
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
