Move tutte_embedding to lib, add bash completion, and fix NixOS setup

- Replace iterative tutte_embedding in lib with numpy direct-solve version from example.py
- Import tutte_embedding into example.py from lib instead of defining it locally
- Fix g._embedding -> g.get_embedding() in outer_face
- Add bash completion to run.sh alongside existing zsh completion
- Use nix-shell -p gcc for plantri build step on NixOS

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

run.sh

@@ -55,7 +55,11 @@ with open("$SCRIPT_DIR/.vscode/settings.json", "w") as f:
     f.write("\n")
 EOF
 
-	make -C "$SCRIPT_DIR/plantri"
+	if command -v nix-shell &>/dev/null; then
+		nix-shell -p gcc --run "make -C \"$SCRIPT_DIR/plantri\""
+	else
+		make -C "$SCRIPT_DIR/plantri"
+	fi
 
 	"$sage_python_path" -m venv "$SCRIPT_DIR/.venv"
 	"$VENV_PYTHON" -m pip install -r "$SCRIPT_DIR/requirements.txt"
@@ -116,7 +120,7 @@ _run_sh() {
           _files
           ;;
         completion)
-          _values 'shell' 'zsh'
+          _values 'shell' 'zsh' 'bash'
           ;;
       esac
       ;;
@@ -124,10 +128,46 @@ _run_sh() {
 }
 
 compdef _run_sh run.sh
+EOF
+		;;
+	bash)
+		cat <<'EOF'
+_run_sh() {
+  local cur prev words cword
+  _init_completion || return
+
+  local subcmds='init_paper setup sage lint completion'
+
+  if [[ $cword -eq 1 ]]; then
+    COMPREPLY=( $(compgen -W "$subcmds" -- "$cur") )
+    return
+  fi
+
+  case ${words[1]} in
+    init_paper)
+      # free-form paper title, no completion
+      ;;
+    setup)
+      case $((cword - 1)) in
+        1) COMPREPLY=( $(compgen -f -- "$cur") ) ;;
+        2) COMPREPLY=( $(compgen -d -- "$cur") ) ;;
+        3) COMPREPLY=() ;;  # system name, free-form
+      esac
+      ;;
+    sage|lint)
+      COMPREPLY=( $(compgen -f -- "$cur") )
+      ;;
+    completion)
+      COMPREPLY=( $(compgen -W 'zsh bash' -- "$cur") )
+      ;;
+  esac
+}
+
+complete -F _run_sh run.sh
 EOF
 		;;
 	*)
-		echo "Unsupported shell: $shell. Supported: zsh" >&2
+		echo "Unsupported shell: $shell. Supported: zsh bash" >&2
 		exit 1
 		;;
 	esac