chore: add, build, tooling, scripts

Batch Justfile audit: standardised naming (lowercase→Justfile),
fixed parse errors, removed useless build-riscv from non-Rust repos,
added missing assail recipe, and fixed code quality issues.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hyperpolymath