fix: add pnpm install to init and pnpm oxlint to lint in justfile

[kazupon]

Summary

• Add pnpm install to just init so that Node.js dependencies (e.g. oxfmt, oxlint) are installed during setup
• Add pnpm oxlint to just lint to run JS/TS linting alongside Clippy

Without pnpm install in init, just ready fails because oxfmt (called by just fmt) is not available.

[kazupon]

I've just noticed that packages/tools is not used.
It seems there’s no longer much point in installing oxlint or oxfmt for this project. 🤔