Implement lazy loading for category examples and improve type safety

[Null000]

Summary

This PR optimizes the category examples loading by implementing lazy initialization and improves type safety throughout the codebase by replacing any types with proper TypeScript types.

Key Changes

• Lazy load category examples: Examples are now generated only when a category group is opened, rather than being created upfront for all categories. This improves initial page load performance.

  • Examples container is created empty initially
  • Examples are populated on the first toggle event when a group is opened
  • Auto-opened groups (with checked items) trigger example generation immediately

• Improved type safety:

  • Changed solved as any[] to solved as string[] in index.ts
  • Changed currentProblem: any to currentProblem: Problem in practice.ts
  • Replaced const dict: any = {} with const dict: Partial<Record<Category, string>> = {} in common.ts with proper type assertion

• Code cleanup:

  • Removed debug console.log() statement from practice.ts
  • Updated comment to clarify that examples container is populated lazily

Implementation Details

The lazy loading is implemented by:

1. Creating an empty .category-examples div for each category
2. Attaching a toggle event listener to the group's <details> element
3. On toggle, querying for empty example containers and populating them with 3 random problems
4. Manually dispatching the toggle event for auto-opened groups to ensure examples are generated

https://claude.ai/code/session_01HG9GdKzqLikbHeTm98p5p8