Sprint 6: JSON file persistence + real SSH terminal + V1 crypto/knownhosts integration

- go.mod replace directive for git.tukangketik.id/swanadiva/hostkeeper → ../../v1
- store/ package: JSON file persistence for hosts, snippets, keys, settings
  (~/Library/Application Support/hostkeeper/v2/)
- model SSH fields: Hostname, Port, Username, AuthType, Password, KeyID
- sshconn/ package: real SSH client via golang.org/x/crypto/ssh
- Terminal WS: real SSH connection with fallback to mock shell
- Dynamic host list in terminal (server-rendered JSON script tag)
- All mock data defaults removed from model packages
- Settings persist via store/settings.go

app/backend/internal/store/key.go

@@ -0,0 +1,94 @@
+package store
+
+import (
+	"time"
+	"git.tukangketik.id/swanadiva/hostkeeper/v2/internal/model"
+)
+
+type KeyStore struct {
+	keys []model.Key
+}
+
+func NewKeyStore() *KeyStore {
+	s := &KeyStore{}
+	mu.RLock()
+	readFile("keys.json", &s.keys)
+	mu.RUnlock()
+	if s.keys == nil {
+		s.keys = []model.Key{}
+	}
+	return s
+}
+
+func (s *KeyStore) All() []model.Key {
+	mu.RLock()
+	defer mu.RUnlock()
+	return s.keys
+}
+
+func (s *KeyStore) Search(q string) []model.Key {
+	mu.RLock()
+	defer mu.RUnlock()
+	if q == "" {
+		return s.keys
+	}
+	var res []model.Key
+	for _, k := range s.keys {
+		if contains(k.Name, q) || contains(k.Username, q) || contains(k.URL, q) {
+			res = append(res, k)
+		}
+	}
+	return res
+}
+
+func (s *KeyStore) Add(name, username, url, passphrase string) model.Key {
+	mu.Lock()
+	defer mu.Unlock()
+	k := model.Key{
+		ID:         randID(),
+		Name:       name,
+		Username:   username,
+		URL:        url,
+		Passphrase: passphrase,
+		Strength:   calcStrength(passphrase),
+		CreatedAt:  time.Now().Format("Jan 2, 2006"),
+	}
+	s.keys = append(s.keys, k)
+	writeFile("keys.json", &s.keys)
+	return k
+}
+
+func (s *KeyStore) Delete(id string) {
+	mu.Lock()
+	defer mu.Unlock()
+	for i, k := range s.keys {
+		if k.ID == id {
+			s.keys = append(s.keys[:i], s.keys[i+1:]...)
+			writeFile("keys.json", &s.keys)
+			return
+		}
+	}
+}
+
+func calcStrength(p string) string {
+	l, d, u, s := 0, 0, 0, 0
+	for _, c := range p {
+		switch {
+		case c >= 'a' && c <= 'z':
+			l++
+		case c >= 'A' && c <= 'Z':
+			u++
+		case c >= '0' && c <= '9':
+			d++
+		default:
+			s++
+		}
+	}
+	if len(p) >= 12 && u >= 1 && d >= 1 && s >= 1 {
+		return "secure"
+	}
+	if len(p) >= 8 && u+d+s >= 2 {
+		return "moderate"
+	}
+	return "weak"
+}