feat: add guide page foundation and routing (refs #203)

- Create GuidePage with responsive layout (sticky TOC sidebar desktop, collapsible accordion mobile)
- Add GuideTableOfContents with scroll-based active section tracking
- Create GuideScreenshot and GuideTable shared components
- Add guideTypes.ts with section metadata for all 10 sections
- Add lazy-loaded /guide route in App.tsx with public access
- Placeholder section components for all 10 guide sections

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

frontend/src/pages/GuidePage/sections/index.ts

@@ -0,0 +1,12 @@
+import { lazy } from 'react';
+
+export const GettingStartedSection = lazy(() => import('./GettingStartedSection').then(m => ({ default: m.GettingStartedSection })));
+export const DashboardSection = lazy(() => import('./DashboardSection').then(m => ({ default: m.DashboardSection })));
+export const VehiclesSection = lazy(() => import('./VehiclesSection').then(m => ({ default: m.VehiclesSection })));
+export const FuelLogsSection = lazy(() => import('./FuelLogsSection').then(m => ({ default: m.FuelLogsSection })));
+export const MaintenanceSection = lazy(() => import('./MaintenanceSection').then(m => ({ default: m.MaintenanceSection })));
+export const GasStationsSection = lazy(() => import('./GasStationsSection').then(m => ({ default: m.GasStationsSection })));
+export const DocumentsSection = lazy(() => import('./DocumentsSection').then(m => ({ default: m.DocumentsSection })));
+export const SettingsSection = lazy(() => import('./SettingsSection').then(m => ({ default: m.SettingsSection })));
+export const SubscriptionSection = lazy(() => import('./SubscriptionSection').then(m => ({ default: m.SubscriptionSection })));
+export const MobileExperienceSection = lazy(() => import('./MobileExperienceSection').then(m => ({ default: m.MobileExperienceSection })));