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/settings.go

@@ -0,0 +1,42 @@
+package store
+
+import "git.tukangketik.id/swanadiva/hostkeeper/v2/internal/model"
+
+type SettingsStore struct {
+	cfg model.AppConfig
+}
+
+func NewSettingsStore() *SettingsStore {
+	s := &SettingsStore{cfg: defaultConfig()}
+	mu.RLock()
+	readFile("settings.json", &s.cfg)
+	mu.RUnlock()
+	return s
+}
+
+func (s *SettingsStore) Get() model.AppConfig {
+	mu.RLock()
+	defer mu.RUnlock()
+	return s.cfg
+}
+
+func (s *SettingsStore) Update(cfg model.AppConfig) {
+	mu.Lock()
+	defer mu.Unlock()
+	s.cfg = cfg
+	writeFile("settings.json", &s.cfg)
+}
+
+func defaultConfig() model.AppConfig {
+	return model.AppConfig{
+		Theme:         "light",
+		FontSize:      14,
+		Scrollback:    5000,
+		AutoLock:      5,
+		Keepalive:     true,
+		CopyOnSelect:  true,
+		BellEnabled:   false,
+		AutoReconnect: true,
+		BlinkCursor:   false,
+	}
+}