feat: add guide navigation integration and tests (refs #203)

- Add Guide link to public nav bar (desktop + mobile) in HomePage
- Add Guide link to authenticated sidebar in Layout.tsx
- Add Guide link to HamburgerDrawer with window.location guard
- Add GuidePage integration tests (6 test scenarios)
- Remove old PDF user guide at public/docs/v2026-01-03.pdf

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

frontend/src/components/Layout.tsx

@@ -14,6 +14,7 @@ import BuildRoundedIcon from '@mui/icons-material/BuildRounded';
 import PlaceRoundedIcon from '@mui/icons-material/PlaceRounded';
 import SettingsRoundedIcon from '@mui/icons-material/SettingsRounded';
 import DescriptionRoundedIcon from '@mui/icons-material/DescriptionRounded';
+import HelpOutlineRoundedIcon from '@mui/icons-material/HelpOutlineRounded';
 import MenuIcon from '@mui/icons-material/Menu';
 import ChevronLeftRoundedIcon from '@mui/icons-material/ChevronLeftRounded';
 import ChevronRightRoundedIcon from '@mui/icons-material/ChevronRightRounded';
@@ -51,6 +52,7 @@ export const Layout: React.FC<LayoutProps> = ({ children, mobileMode = false })
     { name: 'Gas Stations', href: '/garage/stations', icon: <PlaceRoundedIcon sx={{ fontSize: 20 }} /> },
     { name: 'Documents', href: '/garage/documents', icon: <DescriptionRoundedIcon sx={{ fontSize: 20 }} /> },
     { name: 'Settings', href: '/garage/settings', icon: <SettingsRoundedIcon sx={{ fontSize: 20 }} /> },
+    { name: 'Guide', href: '/guide', icon: <HelpOutlineRoundedIcon sx={{ fontSize: 20 }} /> },
   ];
 
   const sidebarWidth = sidebarCollapsed ? 64 : 256;