feat(puzzles): implement puzzle categorization hierarchy and tag system

[Ranjeet2063]

Closes #450

Description

This pull request implements the puzzle categorization and tag system with hierarchy navigation, multi-tag filtering, search support, category analytics, and recommendation mechanisms.

Summary of Changes

• Category Hierarchy Structure:
  • Enhanced Category entity with parent/child relations (parentId, parent, children), slug, icon, displayOrder, and isActive fields.
  • Implemented getHierarchy() in CategoriesService to construct nested category trees.
• Analytics & Recommendations:
  • Implemented getCategoryAnalytics(id?) calculating total puzzles, completions, average ratings, difficulty breakdown, and popularity score.
  • Implemented getRecommendations(limit) ranking categories by activity and popularity score.
• Multi-Tag System & Trending Tags:
  • Implemented getTrendingTags(limit) in TagsService ordering tags by usage frequency.
  • Implemented getRecommendedTags(seeds, limit) for related tag suggestions.
  • Added filterPuzzlesByMultiTags(tags, matchAll) supporting both conjunction and disjunction tag filtering.
• Search & Filtering API:
  • Added searchPuzzlesByCategory() in CategoriesService supporting child category aggregation, multi-tag filtering, and keyword search.
  • Added CategoryFilterDto and CategoryAnalyticsDto with class-validator/transformer validations.
• API Endpoints:
  • Exposed GET /categories/hierarchy, GET /categories/recommendations, GET /categories/:id/analytics, GET /categories/:id/puzzles on CategoriesController.
  • Exposed GET /tags/trending, GET /tags/recommendations on TagsController.
• Unit Testing:
  • Added comprehensive test suite in src/puzzles/tests/puzzle-categorization-tags.spec.ts (100% passing).
  • Verified regression safety with existing tags.service.spec.ts.

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