feat: netssh completion install — user-space shell completion setup

Adds `netssh completion install` subcommand:
- Auto-detects shell from $SHELL, override with --shell bash|zsh|fish
- bash  → ~/.local/share/bash-completion/completions/netssh
- zsh   → ~/.zfunc/_netssh  (prints fpath hint)
- fish  → ~/.config/fish/completions/netssh.fish
- No sudo required

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

cmd/netssh/main.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"os"
+	"path/filepath"
 	"sort"
 	"strings"
 	"text/tabwriter"
@@ -207,11 +208,84 @@ func rootCmd() *cobra.Command {
 		},
 	}
 
-	// cobra automatically adds a "completion" subcommand
+	// cobra automatically adds a "completion" subcommand; we extend it with "install".
 	root.AddCommand(configureCmd(), searchCmd(), cacheCmd())
+
+	for _, cmd := range root.Commands() {
+		if cmd.Name() == "completion" {
+			cmd.AddCommand(completionInstallCmd(root))
+			break
+		}
+	}
+
 	return root
 }
 
+func completionInstallCmd(root *cobra.Command) *cobra.Command {
+	var shell string
+	cmd := &cobra.Command{
+		Use:   "install",
+		Short: "Install shell completion for the current user (no sudo required)",
+		RunE: func(cmd *cobra.Command, args []string) error {
+			if shell == "" {
+				shell = filepath.Base(os.Getenv("SHELL"))
+			}
+
+			var (
+				dir  string
+				file string
+				gen  func() ([]byte, error)
+				note string
+			)
+
+			switch shell {
+			case "bash":
+				dir = filepath.Join(os.Getenv("HOME"), ".local", "share", "bash-completion", "completions")
+				file = filepath.Join(dir, "netssh")
+				gen = func() ([]byte, error) {
+					var buf strings.Builder
+					return []byte(buf.String()), root.GenBashCompletionV2(&buf, true)
+				}
+				note = "Reload your shell or run: source " + file
+			case "zsh":
+				dir = filepath.Join(os.Getenv("HOME"), ".zfunc")
+				file = filepath.Join(dir, "_netssh")
+				gen = func() ([]byte, error) {
+					var buf strings.Builder
+					return []byte(buf.String()), root.GenZshCompletion(&buf)
+				}
+				note = "Make sure ~/.zfunc is in your fpath:\n  fpath=(~/.zfunc $fpath)\n  autoload -Uz compinit && compinit"
+			case "fish":
+				configDir, _ := os.UserConfigDir()
+				dir = filepath.Join(configDir, "fish", "completions")
+				file = filepath.Join(dir, "netssh.fish")
+				gen = func() ([]byte, error) {
+					var buf strings.Builder
+					return []byte(buf.String()), root.GenFishCompletion(&buf, true)
+				}
+				note = "Reload your shell or start a new fish session."
+			default:
+				return fmt.Errorf("unsupported shell %q — use --shell bash|zsh|fish", shell)
+			}
+
+			script, err := gen()
+			if err != nil {
+				return fmt.Errorf("generating completion: %w", err)
+			}
+			if err := os.MkdirAll(dir, 0o755); err != nil {
+				return fmt.Errorf("creating %s: %w", dir, err)
+			}
+			if err := os.WriteFile(file, script, 0o644); err != nil {
+				return fmt.Errorf("writing %s: %w", file, err)
+			}
+			fmt.Printf("Completion installed → %s\n%s\n", file, note)
+			return nil
+		},
+	}
+	cmd.Flags().StringVar(&shell, "shell", "", "Shell to install for (default: $SHELL). Supported: bash, zsh, fish")
+	return cmd
+}
+
 func configureCmd() *cobra.Command {
 	return &cobra.Command{
 		Use:   "configure",