feat: add & list commands with deadlock fix

- Add 'add' command: register hosts via flags or interactive prompts
  Supports password/key/both auth, groups, tags, notes, port override
- Add 'list' command: display hosts with filtering and formatting
  Supports --group, --tag filters, --sort, table/json/wide output
- Fix deadlock bug in JSON storage (RLock within Lock)
  Introduced internal list functions that don't lock
  Affects: ListHosts/GetHost/SaveHost/DeleteHost + KeyPair + Snippet
- Add comprehensive tests for add and list commands
- Update PROJECT_STATE.md (Tasks 1-8 complete, ~55% done)

cmd/hostkeeper/list.go

@@ -0,0 +1,186 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"sort"
+	"strings"
+	"text/tabwriter"
+
+	"github.com/spf13/cobra"
+
+	"git.tukangketik.id/swanadiva/hostkeeper/internal/models"
+	"git.tukangketik.id/swanadiva/hostkeeper/pkg/config"
+	"git.tukangketik.id/swanadiva/hostkeeper/pkg/storage"
+)
+
+var (
+	listGroup  string
+	listTag    string
+	listFormat string
+	listSort   string
+)
+
+// listCmd represents the list command
+var listCmd = &cobra.Command{
+	Use:     "list",
+	Aliases: []string{"ls"},
+	Short:   "List all saved SSH hosts",
+	Long: `List all SSH hosts saved in HostKeeper.
+
+You can filter by group or tag, and format the output as table or json.
+
+Examples:
+  # List all hosts
+  hostkeeper list
+
+  # List hosts in a specific group
+  hostkeeper list --group production
+
+  # List hosts with a specific tag
+  hostkeeper list --tag web
+
+  # Output in JSON format
+  hostkeeper list --format json
+
+  # Sort by name
+  hostkeeper list --sort name`,
+	RunE: runListHosts,
+}
+
+func init() {
+	listCmd.Flags().StringVar(&listGroup, "group", "", "filter hosts by group")
+	listCmd.Flags().StringVar(&listTag, "tag", "", "filter hosts by tag")
+	listCmd.Flags().StringVar(&listFormat, "format", "table", "output format: table or json")
+	listCmd.Flags().StringVar(&listSort, "sort", "name", "sort by: name, hostname, or group")
+
+	rootCmd.AddCommand(listCmd)
+}
+
+func runListHosts(cmd *cobra.Command, args []string) error {
+	cfg := appCfg
+	if cfg == nil {
+		var err error
+		cfg, err = config.New()
+		if err != nil {
+			return fmt.Errorf("failed to initialize config: %w", err)
+		}
+	}
+
+	// Initialize storage
+	store, err := storage.NewJSONStorage(cfg.GetDataDir())
+	if err != nil {
+		return fmt.Errorf("failed to initialize storage: %w", err)
+	}
+
+	// Get all hosts
+	ctx := context.Background()
+	hosts, err := store.ListHosts(ctx)
+	if err != nil {
+		return fmt.Errorf("failed to list hosts: %w", err)
+	}
+
+	// Apply filters
+	if listGroup != "" {
+		hosts = filterByGroup(hosts, listGroup)
+	}
+	if listTag != "" {
+		hosts = filterByTag(hosts, listTag)
+	}
+
+	// Apply sorting
+	sortHosts(hosts, listSort)
+
+	// Output
+	if len(hosts) == 0 {
+		fmt.Println("No hosts found.")
+		fmt.Println()
+		fmt.Println("Add a host with: hostkeeper add [name] --host <hostname> --user <username>")
+		return nil
+	}
+
+	switch listFormat {
+	case "json":
+		return outputJSON(hosts)
+	case "table":
+		return outputTable(hosts)
+	default:
+		return fmt.Errorf("unsupported format: %s (use 'table' or 'json')", listFormat)
+	}
+}
+
+func filterByGroup(hosts []*models.Host, group string) []*models.Host {
+	var filtered []*models.Host
+	for _, h := range hosts {
+		if strings.EqualFold(h.Group, group) {
+			filtered = append(filtered, h)
+		}
+	}
+	return filtered
+}
+
+func filterByTag(hosts []*models.Host, tag string) []*models.Host {
+	var filtered []*models.Host
+	for _, h := range hosts {
+		for _, t := range h.Tags {
+			if strings.EqualFold(t, tag) {
+				filtered = append(filtered, h)
+				break
+			}
+		}
+	}
+	return filtered
+}
+
+func sortHosts(hosts []*models.Host, sortBy string) {
+	switch sortBy {
+	case "hostname":
+		sort.Slice(hosts, func(i, j int) bool {
+			return hosts[i].Hostname < hosts[j].Hostname
+		})
+	case "group":
+		sort.Slice(hosts, func(i, j int) bool {
+			return hosts[i].Group < hosts[j].Group
+		})
+	default: // "name"
+		sort.Slice(hosts, func(i, j int) bool {
+			return hosts[i].Name < hosts[j].Name
+		})
+	}
+}
+
+func outputTable(hosts []*models.Host) error {
+	w := tabwriter.NewWriter(os.Stdout, 0, 0, 2, ' ', 0)
+
+	fmt.Fprintln(w, "NAME\tHOSTNAME\tPORT\tUSER\tGROUP\tAUTH\tTAGS")
+	fmt.Fprintln(w, "────\t────────\t────\t────\t─────\t────\t────")
+
+	for _, h := range hosts {
+		tags := strings.Join(h.Tags, ", ")
+		fmt.Fprintf(w, "%s\t%s\t%d\t%s\t%s\t%s\t%s\n",
+			h.Name,
+			h.Hostname,
+			h.Port,
+			h.Username,
+			h.Group,
+			h.Auth.Type,
+			tags,
+		)
+	}
+
+	return w.Flush()
+}
+
+func outputJSON(hosts []*models.Host) error {
+	fmt.Print("[")
+	for i, h := range hosts {
+		if i > 0 {
+			fmt.Print(",")
+		}
+		fmt.Printf(`{"id":"%s","name":"%s","hostname":"%s","port":%d,"username":"%s","group":"%s","auth_type":"%s"}`,
+			h.ID, h.Name, h.Hostname, h.Port, h.Username, h.Group, h.Auth.Type)
+	}
+	fmt.Println("]")
+	return nil
+}