fix: Correct nested navigation implementation

The previous implementation had a critical flaw in how it tracked section
hierarchies. Section headers in MkDocs nav are just labels, not pages.

Changes:
- Added sectionHierarchy tracking to map section names to parent sections
- Modified traverse() to build section hierarchy while parsing nav
- Updated syncPages() to use section hierarchy for proper parent assignment
- The first page in a section now correctly represents that section
- Child sections properly reference their parent section's first page
- Fixed orphan page handling to process even when no local pages exist

Example flow:
  nav:
    - Guides:
      - Start: start.md
      - Advanced:
        - Config: config.md

Result:
  Home (id=100)
    - Start (id=101, represents 'Guides')
      - Config (id=102, child of 'Start' which represents 'Advanced')

All tests passing (148/148) with proper hierarchy support.

Author: agpenton

.github/copilot/instructions/angular.instructions.md

@@ -0,0 +1,104 @@
+---
+description: 'Angular-specific coding standards and best practices'
+applyTo: '**/*.ts, **/*.html, **/*.scss, **/*.css'
+---
+
+# Angular Development Instructions
+
+Instructions for generating high-quality Angular applications with TypeScript, using Angular Signals for state management, adhering to Angular best practices as outlined at https://angular.dev.
+
+## Project Context
+- Latest Angular version (use standalone components by default)
+- TypeScript for type safety
+- Angular CLI for project setup and scaffolding
+- Follow Angular Style Guide (https://angular.dev/style-guide)
+- Use Angular Material or other modern UI libraries for consistent styling (if specified)
+
+## Development Standards
+
+### Architecture
+- Use standalone components unless modules are explicitly required
+- Organize code by standalone feature modules or domains for scalability
+- Implement lazy loading for feature modules to optimize performance
+- Use Angular's built-in dependency injection system effectively
+- Structure components with a clear separation of concerns (smart vs. presentational components)
+
+### TypeScript
+- Enable strict mode in `tsconfig.json` for type safety
+- Define clear interfaces and types for components, services, and models
+- Use type guards and union types for robust type checking
+- Implement proper error handling with RxJS operators (e.g., `catchError`)
+- Use typed forms (e.g., `FormGroup`, `FormControl`) for reactive forms
+
+### Component Design
+- Follow Angular's component lifecycle hooks best practices
+- When using Angular >= 19, Use `input()` `output()`, `viewChild()`, `viewChildren()`, `contentChild()` and `contentChildren()` functions instead of decorators; otherwise use decorators
+- Leverage Angular's change detection strategy (default or `OnPush` for performance)
+- Keep templates clean and logic in component classes or services
+- Use Angular directives and pipes for reusable functionality
+
+### Styling
+- Use Angular's component-level CSS encapsulation (default: ViewEncapsulation.Emulated)
+- Prefer SCSS for styling with consistent theming
+- Implement responsive design using CSS Grid, Flexbox, or Angular CDK Layout utilities
+- Follow Angular Material's theming guidelines if used
+- Maintain accessibility (a11y) with ARIA attributes and semantic HTML
+
+### State Management
+- Use Angular Signals for reactive state management in components and services
+- Leverage `signal()`, `computed()`, and `effect()` for reactive state updates
+- Use writable signals for mutable state and computed signals for derived state
+- Handle loading and error states with signals and proper UI feedback
+- Use Angular's `AsyncPipe` to handle observables in templates when combining signals with RxJS
+
+### Data Fetching
+- Use Angular's `HttpClient` for API calls with proper typing
+- Implement RxJS operators for data transformation and error handling
+- Use Angular's `inject()` function for dependency injection in standalone components
+- Implement caching strategies (e.g., `shareReplay` for observables)
+- Store API response data in signals for reactive updates
+- Handle API errors with global interceptors for consistent error handling
+
+### Security
+- Sanitize user inputs using Angular's built-in sanitization
+- Implement route guards for authentication and authorization
+- Use Angular's `HttpInterceptor` for CSRF protection and API authentication headers
+- Validate form inputs with Angular's reactive forms and custom validators
+- Follow Angular's security best practices (e.g., avoid direct DOM manipulation)
+
+### Performance
+- Enable production builds with `ng build --prod` for optimization
+- Use lazy loading for routes to reduce initial bundle size
+- Optimize change detection with `OnPush` strategy and signals for fine-grained reactivity
+- Use trackBy in `ngFor` loops to improve rendering performance
+- Implement server-side rendering (SSR) or static site generation (SSG) with Angular Universal (if specified)
+
+### Testing
+- Write unit tests for components, services, and pipes using Jasmine and Karma
+- Use Angular's `TestBed` for component testing with mocked dependencies
+- Test signal-based state updates using Angular's testing utilities
+- Write end-to-end tests with Cypress or Playwright (if specified)
+- Mock HTTP requests using `provideHttpClientTesting`
+- Ensure high test coverage for critical functionality
+
+## Implementation Process
+1. Plan project structure and feature modules
+2. Define TypeScript interfaces and models
+3. Scaffold components, services, and pipes using Angular CLI
+4. Implement data services and API integrations with signal-based state
+5. Build reusable components with clear inputs and outputs
+6. Add reactive forms and validation
+7. Apply styling with SCSS and responsive design
+8. Implement lazy-loaded routes and guards
+9. Add error handling and loading states using signals
+10. Write unit and end-to-end tests
+11. Optimize performance and bundle size
+
+## Additional Guidelines
+- Follow the Angular Style Guide for file naming conventions (see https://angular.dev/style-guide), e.g., use `feature.ts` for components and `feature-service.ts` for services. For legacy codebases, maintain consistency with existing pattern.
+- Use Angular CLI commands for generating boilerplate code
+- Document components and services with clear JSDoc comments
+- Ensure accessibility compliance (WCAG 2.1) where applicable
+- Use Angular's built-in i18n for internationalization (if specified)
+- Keep code DRY by creating reusable utilities and shared modules
+- Use signals consistently for state management to ensure reactive updates