refactor: use automd for README updates

[onmax]

Summary

Replace manual README update logic with automd for file includes

Changes

• Add automd as dev dependency
• Use automd for <\!-- automd:file --> markers (apps, resources, exchanges, explorers, RPC)
• Keep custom TOC generator (automd does not have native TOC yet - PR#72 open)
• Reduce README update code from ~130 lines to ~30 lines
• Simplify comments (focus on why, not what)
• Add Nimiq Hub logo to README header

Benefits

• Cleaner, maintainable code
• Leverages automd file inclusion system
• Same script pattern: validation → API fetch → markdown gen → README update
• GitHub workflow unchanged

Test plan

• Build passes
• Lint passes
• README correctly updated with all sections
• TOC generated properly