feat: add project export and import functionality

- Implemented `pcli project export` command to export project hierarchy as JSON.
- Added `pcli project import` command to import project data from JSON.
- Created user client to fetch user details for comment attribution.
- Introduced new data structures for export and import processes.
- Ensured name-based references in exports and handled conflicts during imports.
- Added versioning and progress reporting for import operations.
- Updated documentation and specifications for new features.

client/users.go

@@ -0,0 +1,26 @@
+package client
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+
+	"git.franklin.lab/steve.cliff/pcli/model"
+)
+
+func (c *Client) ListUsers(ctx context.Context) ([]model.User, error) {
+	data, err := c.DoNoBody(ctx, "GET", "/api/users")
+	if err != nil {
+		return nil, err
+	}
+
+	var response struct {
+		Items []model.User `json:"items"`
+	}
+
+	if err := json.Unmarshal(data, &response); err != nil {
+		return nil, fmt.Errorf("failed to unmarshal users response: %w", err)
+	}
+
+	return response.Items, nil
+}