refactor: move V1 code into v1/ subdirectory

- git mv cmd/ internal/ pkg/ test/ go.mod go.sum Makefile build.sh docs/ v1/
- Create v1/README.md with V1 documentation
- Update root README for V1 + V2 structure
- V1 still builds (cd v1 && go build ./cmd/hostkeeper) and 105 tests pass
- Root is now clean for V2 development

v1/pkg/storage/storage.go

@@ -0,0 +1,49 @@
+package storage
+
+import (
+	"context"
+
+	"git.tukangketik.id/swanadiva/hostkeeper/internal/models"
+)
+
+// Storage defines the interface for data persistence
+type Storage interface {
+	// Host operations
+	ListHosts(ctx context.Context) ([]*models.Host, error)
+	GetHost(ctx context.Context, id string) (*models.Host, error)
+	SaveHost(ctx context.Context, host *models.Host) error
+	DeleteHost(ctx context.Context, id string) error
+
+	// KeyPair operations
+	ListKeyPairs(ctx context.Context) ([]*models.KeyPair, error)
+	GetKeyPair(ctx context.Context, id string) (*models.KeyPair, error)
+	SaveKeyPair(ctx context.Context, keyPair *models.KeyPair) error
+	DeleteKeyPair(ctx context.Context, id string) error
+
+	// Snippet operations
+	ListSnippets(ctx context.Context) ([]*models.Snippet, error)
+	GetSnippet(ctx context.Context, id string) (*models.Snippet, error)
+	SaveSnippet(ctx context.Context, snippet *models.Snippet) error
+	DeleteSnippet(ctx context.Context, id string) error
+
+	// Export/Import
+	ExportData(ctx context.Context) (*ExportData, error)
+	ImportData(ctx context.Context, data *ExportData, strategy MergeStrategy) error
+}
+
+// ExportData represents the data structure for export/import
+type ExportData struct {
+	Hosts    []*models.Host    `json:"hosts"`
+	KeyPairs []*models.KeyPair `json:"key_pairs"`
+	Snippets []*models.Snippet `json:"snippets"`
+}
+
+// MergeStrategy defines how imported data is merged with existing data
+type MergeStrategy string
+
+const (
+	// MergeStrategyReplace replaces all existing data with imported data
+	MergeStrategyReplace MergeStrategy = "replace"
+	// MergeStrategyMerge keeps existing data and adds only new items
+	MergeStrategyMerge MergeStrategy = "merge"
+)