feat: add alias file generation and management for shell hooks

- **Aliases**: Generate shell alias files (`aliases.sh` for bash/zsh, `netssh.fish` for fish) from cached hosts. Regenerate on each shell startup and cache refresh to keep aliases updated.
- **Hooks**: Extend shell hook functionality to include alias file support. Install and uninstall commands updated for bash, zsh, and fish.
- **Tests**: Add unit tests to verify alias file generation, path resolution, and idempotent hook installation.
- **Docs**: Update README with instructions for alias file usage, installation, and relation to hooks.

internal/hook/aliases.go

@@ -0,0 +1,82 @@
+package hook
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// AliasEntry holds a single shell alias mapping.
+type AliasEntry struct {
+	Name string // short alias name (e.g. "web01")
+	Host string // canonical NetBox hostname (e.g. "web01.example.com")
+}
+
+// AliasesPath returns the path for the bash/zsh aliases file.
+func AliasesPath() string {
+	cacheDir, err := os.UserCacheDir()
+	if err != nil {
+		cacheDir = filepath.Join(os.Getenv("HOME"), ".cache")
+	}
+	return filepath.Join(cacheDir, "netssh", "aliases.sh")
+}
+
+// FishAliasesPath returns the path for the fish conf.d aliases file.
+// Fish auto-sources every file in conf.d, so no explicit source line is needed.
+func FishAliasesPath() string {
+	configDir, err := os.UserConfigDir()
+	if err != nil {
+		configDir = filepath.Join(os.Getenv("HOME"), ".config")
+	}
+	return filepath.Join(configDir, "fish", "conf.d", "netssh.fish")
+}
+
+// WriteAliasFiles writes alias definitions to disk for all supported shells.
+//
+// The bash/zsh file (~/.cache/netssh/aliases.sh) is always written.
+// The fish file (~/.config/fish/conf.d/netssh.fish) is written only when
+// ~/.config/fish/ already exists (i.e. fish is configured on this system).
+func WriteAliasFiles(entries []AliasEntry) error {
+	if err := writeShAliasFile(entries); err != nil {
+		return err
+	}
+	writeFishAliasFile(entries) // best-effort — never blocks the caller on failure
+	return nil
+}
+
+func writeShAliasFile(entries []AliasEntry) error {
+	p := AliasesPath()
+	if err := os.MkdirAll(filepath.Dir(p), 0o755); err != nil {
+		return fmt.Errorf("creating aliases dir: %w", err)
+	}
+	var b strings.Builder
+	b.WriteString("# netssh aliases — generated automatically, do not edit\n")
+	b.WriteString("# Regenerated on every shell start and after 'netssh cache refresh'.\n")
+	for _, e := range entries {
+		fmt.Fprintf(&b, "alias %s='netssh %s'\n", e.Name, e.Host)
+	}
+	return os.WriteFile(p, []byte(b.String()), 0o644)
+}
+
+func writeFishAliasFile(entries []AliasEntry) {
+	configDir, err := os.UserConfigDir()
+	if err != nil {
+		return
+	}
+	// Only write if fish is configured on this system.
+	if _, err := os.Stat(filepath.Join(configDir, "fish")); err != nil {
+		return
+	}
+	p := FishAliasesPath()
+	if err := os.MkdirAll(filepath.Dir(p), 0o755); err != nil {
+		return
+	}
+	var b strings.Builder
+	b.WriteString("# netssh aliases — generated automatically, do not edit\n")
+	b.WriteString("# Regenerated on every shell start and after 'netssh cache refresh'.\n")
+	for _, e := range entries {
+		fmt.Fprintf(&b, "alias %s 'netssh %s'\n", e.Name, e.Host)
+	}
+	os.WriteFile(p, []byte(b.String()), 0o644) //nolint:errcheck
+}