feat: add temporary learning resources to "start track" buttons

I noticed that the Learning Tracks section (Frontend Fundamentals, Modern React, Backend Engineering) includes "Start Track" buttons, but currently these buttons do not lead to any learning resources or pages.

**Suggestion**
While a full learning platform or curriculum system may still be under development, we could temporarily improve the user experience by linking these tracks to curated learning resources, such as high-quality YouTube tutorials or playlists.

This would allow community members to start learning immediately while the full system is being built.

**Example approach**
Each track could link to a curated set of beginner/intermediate/advanced resources:

- [ ] Frontend Fundamentals
- [ ] HTML & CSS fundamentals
- [ ] JavaScript basics
- [ ] DOM manipulation
- [ ] Modern React
- [ ] React fundamentals
- [ ] React Hooks
- [ ] Next.js basics
- [ ] Tailwind CSS
- [ ] Backend Engineering
- [ ] Node.js fundamentals
- [ ] API development
- [ ] PostgreSQL basics
- [ ] Docker introduction

These could initially point to trusted YouTube playlists or external documentation, and later be replaced with a dedicated learning platform or internal resources.

**Benefits**
1. Prevents the buttons from leading to empty or inactive pages
2. Provides immediate value to community members
3. Keeps the section functional until the full learning system is implemented

If this approach makes sense, I’d be happy to help:
curate resources, or implement the temporary links for each track.

Thanks!

Start by locating the Learning Tracks section and its three “Start Track” buttons in the TypeScript web project. Review how the buttons currently behave, choose the curated resources for Frontend Fundamentals, Modern React, and Backend Engineering, and consider the work done when each button leads to useful learning material.

Written by the indexing model from the issue text.