chore: update developer roadmap study materials for 2026 - #227

Changed pages include:

• index.html - view
• 404.html - view
• roadmap.html - view
• advices.html - view
• roadmaps/ai/artificial-intelligence.html - view
• roadmaps/backend/backend.html - view
• roadmaps/data/data-engineering.html - view
• roadmaps/devops/devops.html - view
• roadmaps/frontend/frontend.html - view
• roadmaps/fullstack/fullstack.html - view

There are more changes not included in the list