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/cache/cache.go

@@ -20,10 +20,11 @@ type Entry struct {
 }
 
 type Cache struct {
-	mu      sync.RWMutex
-	entries map[string]Entry
-	path    string
-	ttl     time.Duration
+	mu           sync.RWMutex
+	entries      map[string]Entry
+	path         string
+	ttl          time.Duration
+	refreshStamp string // path to last_refresh timestamp file
 }
 
 type diskFormat struct {
@@ -31,11 +32,48 @@ type diskFormat struct {
 }
 
 func New(path string, ttlSeconds int) *Cache {
-	return &Cache{
-		entries: make(map[string]Entry),
-		path:    path,
-		ttl:     time.Duration(ttlSeconds) * time.Second,
+	stamp := ""
+	if path != "" {
+		stamp = filepath.Join(filepath.Dir(path), "last_refresh")
 	}
+	return &Cache{
+		entries:      make(map[string]Entry),
+		path:         path,
+		ttl:          time.Duration(ttlSeconds) * time.Second,
+		refreshStamp: stamp,
+	}
+}
+
+// NeedsRefresh reports whether the last full cache refresh (via `cache refresh`)
+// is older than d, or has never happened. Always returns false when no path is set.
+func (c *Cache) NeedsRefresh(d time.Duration) bool {
+	if c.refreshStamp == "" {
+		return false
+	}
+	data, err := os.ReadFile(c.refreshStamp)
+	if err != nil {
+		return true // file missing → never refreshed
+	}
+	var t time.Time
+	if err := t.UnmarshalText(data); err != nil {
+		return true
+	}
+	return time.Since(t) >= d
+}
+
+// SetRefreshed records the current time as the last successful full refresh.
+func (c *Cache) SetRefreshed() error {
+	if c.refreshStamp == "" {
+		return nil
+	}
+	data, err := time.Now().MarshalText()
+	if err != nil {
+		return err
+	}
+	if err := os.MkdirAll(filepath.Dir(c.refreshStamp), 0o755); err != nil {
+		return err
+	}
+	return os.WriteFile(c.refreshStamp, data, 0o644)
 }
 
 func (c *Cache) Load() error {
@@ -137,6 +175,21 @@ func (c *Cache) Search(prefix string) []Entry {
 	return out
 }
 
+// GetByShortcut scans all entries and returns the first whose normalized name matches
+// the normalized shortcut. Returns (entry, found, fresh).
+func (c *Cache) GetByShortcut(shortcut string, normalize func(string) string) (entry Entry, found bool, fresh bool) {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	norm := normalize(shortcut)
+	for _, e := range c.entries {
+		if normalize(e.Name) == norm {
+			isFresh := c.ttl > 0 && time.Since(e.CachedAt) < c.ttl
+			return e, true, isFresh
+		}
+	}
+	return Entry{}, false, false
+}
+
 // Get returns an entry and reports whether it is still within the TTL.
 func (c *Cache) Get(name string) (entry Entry, fresh bool) {
 	c.mu.RLock()