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/handler/keychain.go

@@ -2,10 +2,10 @@ package handler
 
 import (
 	"github.com/gofiber/fiber/v2"
-	"git.tukangketik.id/swanadiva/hostkeeper/v2/internal/model"
+	"git.tukangketik.id/swanadiva/hostkeeper/v2/internal/store"
 )
 
-var keyStore = model.NewKeyStore()
+var keyStore = store.NewKeyStore()
 
 func Keychain(c *fiber.Ctx) error {
 	keys := keyStore.All()