Aligns CONTRIBUTING.md, README.md, README.zh.md, SELF_HOSTING_ADVANCED.md and scripts/dev.sh with the Node 22 / pnpm 10.28.2 / Go 1.26.1 versions used by CI, and adds .nvmrc plus engines.node so version managers and package tooling flag Node 20 early.
Closes#6972
Simplifies local development from 3+ commands to a single `make dev`
that auto-detects environment (main/worktree), creates env files,
installs dependencies, starts PostgreSQL, runs migrations, and launches
both backend and frontend.
Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>