docs: enhance learn section with blog content

- Add hero images to global-payouts, tokenized-deposits, modern-transactions, native-stablecoins
- Add concrete $1,000 cost example with 60-80% savings breakdown to global-payouts
- Add evaluation framework and FAQs to global-payouts
- Add use cases section and partner ecosystem to modern-transactions
- Add custom stablecoin use cases and infrastructure partners to native-stablecoins
- Add key questions and FAQs to tokenized-deposits
- Port 18 SVG illustrations from tempo-web blog posts

Amp-Thread-ID: https://ampcode.com/threads/T-019bdc00-70dd-71fa-a4e5-608e0621bf15
Co-authored-by: Amp <amp@ampcode.com>

Author: snario