Restructure index page to 15 comprehensive life categories (#45)

Replace 5-category structure with systematic 15-category worldview:
1. Mind & Psychology
2. Body & Health
3. Relationships & Communication
4. Economics & Finance
5. Work & Career
6. Technology & Computing
7. Languages
8. Science & Mathematics
9. Philosophy & Worldview
10. History & Civilization
11. Society & Politics
12. Practical Skills
13. Geography & Environment
14. Arts & Culture
15. Entertainment & Leisure

Each category includes a Russian description of its scope.
Existing articles redistributed to appropriate new categories.

Co-authored-by: Claude <noreply@anthropic.com>

Author: streamcode9