fix: migrate JSR dependency from legacy npm:@jsr/ to native jsr: protocol

fix: migrate JSR dependency from legacy npm:@jsr/ to native jsr: protocol

Replace the legacy npm compatibility layer approach with pnpm's native
jsr: protocol support (available since pnpm 10.9.0) to fix 404 errors
when fetching @jsr/std__assert tarballs from npm.jsr.io.

- package.json: use jsr:@std/expect specifier instead of npm:@jsr/std__expect
- package.json, ui/web/package.json: bump engines.pnpm to >=10.9.0
- .npmrc: remove @jsr:registry=https://npm.jsr.io (no longer needed)
- pnpm-lock.yaml: regenerated with native JSR resolution