feat: add NixOS support, Go, and Ruby on Rails; remove Rust

- Add nixos/ directory with declarative flake.nix and home.nix for NixOS
- Make all setup scripts NixOS-aware with proper detection and early exit
- Update bashrc, zshrc, and aliases with Go, Ruby on Rails, and Nix profile paths
- Replace Rust/Cargo references in shell configs with rbenv/Ruby on Rails
- Update README with NixOS quick start and full documentation

aliases.bash

@@ -34,6 +34,25 @@ alias py3='python3'
 alias python='python3'
 alias pip='pip3'
 
+# ── Go ──────────────────────────────────────────────────
+alias gorun='go run'
+alias gobuild='go build'
+alias gotest='go test ./...'
+alias gotidy='go mod tidy'
+alias gofmt='go fmt ./...'
+
+# ── Ruby on Rails ──────────────────────────────────────
+alias be='bundle exec'
+alias bi='bundle install'
+alias bu='bundle update'
+alias rdm='rails db:migrate'
+alias rdr='rails db:rollback'
+alias rds='rails db:seed'
+alias rrg='rails generate'
+alias rrc='rails console'
+alias rrs='rails server'
+alias rroutes='rails routes'
+
 # Pretty print the path
 alias path='echo $PATH | tr -s ":" "\n"'