Reorganize docs around Diataxis and update Mint setup

[odyslam]

Summary

• reorganize the docs navigation and high-traffic pages around the Diataxis framework
• replace user-facing dapp terminology with platform language and point platform flows to app.phylax.systems
• normalize Assertions Book leaf pages into repeatable reference and case-study templates
• pin the project to Node 24 and update Mint while removing the old mise config

Testing

• pnpm exec mint broken-links