feat: introduce shortcuts and shell hook support

- **Shortcuts**: Add hostname normalization with domain stripping and hyphen folding. Include alias generation for cached hosts.
- **Shell Hook**: Automate 24h cache refresh trigger with shell startup hook. Add install/uninstall commands for bash, zsh, and fish.
- **Wizard**: Extend setup wizard to configure shortcuts (domains, hyphen stripping) and default SSH port.
- **Cache**: Add `GetByShortcut` for resolving hosts via normalized shortcuts. Implement `NeedsRefresh` / `SetRefreshed` logic for refresh timestamps.
- **Tests**: Comprehensive unit tests for shortcuts, hook installation, cache refresh, and alias generation.
- **Docs**: Update README with shortcuts, shell hook, and default SSH port configuration.

internal/hook/hook.go

@@ -0,0 +1,101 @@
+package hook
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+const (
+	// Marker is the unique string used to detect an existing hook installation.
+	Marker = "netssh shell-init"
+	// Line is the full line written into the shell profile.
+	Line = "netssh shell-init  # netssh cache auto-refresh"
+)
+
+// ProfilePath returns the canonical shell profile path for the given shell name.
+func ProfilePath(shell string) (string, error) {
+	switch shell {
+	case "bash":
+		return filepath.Join(os.Getenv("HOME"), ".bashrc"), nil
+	case "zsh":
+		return filepath.Join(os.Getenv("HOME"), ".zshrc"), nil
+	case "fish":
+		configDir, err := os.UserConfigDir()
+		if err != nil {
+			configDir = filepath.Join(os.Getenv("HOME"), ".config")
+		}
+		return filepath.Join(configDir, "fish", "config.fish"), nil
+	default:
+		return "", fmt.Errorf("unsupported shell %q — supported: bash, zsh, fish", shell)
+	}
+}
+
+// ReloadNote returns the shell-specific hint for reloading the profile.
+func ReloadNote(profilePath string) string {
+	return "Reload with: source " + profilePath
+}
+
+// IsInstalled reports whether the hook marker is present in the profile file.
+// Returns false if the file does not exist or cannot be read.
+func IsInstalled(profilePath string) bool {
+	data, err := os.ReadFile(profilePath)
+	if err != nil {
+		return false
+	}
+	return strings.Contains(string(data), Marker)
+}
+
+// Install appends the hook line to the profile if it is not already present.
+// Returns (true, nil) when newly installed, (false, nil) when already present.
+// Creates the profile file (and any parent directories) if they do not exist.
+func Install(profilePath string) (installed bool, err error) {
+	if IsInstalled(profilePath) {
+		return false, nil
+	}
+	if err := os.MkdirAll(filepath.Dir(profilePath), 0o755); err != nil {
+		return false, fmt.Errorf("creating directory: %w", err)
+	}
+	f, err := os.OpenFile(profilePath, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0o644)
+	if err != nil {
+		return false, fmt.Errorf("opening profile: %w", err)
+	}
+	defer f.Close()
+	if _, err := fmt.Fprintf(f, "\n%s\n", Line); err != nil {
+		return false, err
+	}
+	return true, nil
+}
+
+// Uninstall removes the hook line from the profile.
+// Returns (true, nil) when removed, (false, nil) when the hook was not found.
+// Returns (false, nil) — not an error — when the file does not exist.
+func Uninstall(profilePath string) (removed bool, err error) {
+	data, err := os.ReadFile(profilePath)
+	if os.IsNotExist(err) {
+		return false, nil
+	}
+	if err != nil {
+		return false, fmt.Errorf("reading profile: %w", err)
+	}
+	content := string(data)
+	if !strings.Contains(content, Marker) {
+		return false, nil
+	}
+
+	var kept []string
+	for _, line := range strings.Split(content, "\n") {
+		if strings.Contains(line, Marker) {
+			continue
+		}
+		kept = append(kept, line)
+	}
+	// Collapse triple blank lines that the removal may leave.
+	cleaned := strings.ReplaceAll(strings.Join(kept, "\n"), "\n\n\n", "\n\n")
+
+	if err := os.WriteFile(profilePath, []byte(cleaned), 0o644); err != nil {
+		return false, fmt.Errorf("writing profile: %w", err)
+	}
+	return true, nil
+}