Implement Checklist operations

Add checklists.go with ChecklistService for CRUD operations:
- client.Checklists() returns ChecklistService
- List(ctx) - get all checklists (GET /checklists.json)
- ListWithOptions(ctx, opts) - with archived filter support
- Get(ctx, id) - get single checklist (GET /checklists/{id}.json)
- Create(ctx, name) - create new checklist (POST /checklists.json)
- Update(ctx, id, name) - update checklist name (PUT /checklists/{id}.json)
- Delete(ctx, id) - delete checklist (DELETE /checklists/{id}.json)

All methods support context for cancellation and timeouts.

Closes checkvist-api-c2k

checklists.go

@@ -1,3 +1,93 @@
 package checkvist
 
+import (
+	"context"
+	"fmt"
+)
+
 // checklists.go contains the ChecklistService for CRUD operations on checklists.
+
+// ChecklistService provides operations on Checkvist checklists.
+type ChecklistService struct {
+	client *Client
+}
+
+// Checklists returns a ChecklistService for performing checklist operations.
+func (c *Client) Checklists() *ChecklistService {
+	return &ChecklistService{client: c}
+}
+
+// ListOptions configures the List operation.
+type ListOptions struct {
+	// Archived filters to show only archived checklists when true.
+	Archived bool
+}
+
+// List returns all checklists accessible to the authenticated user.
+func (s *ChecklistService) List(ctx context.Context) ([]Checklist, error) {
+	return s.ListWithOptions(ctx, ListOptions{})
+}
+
+// ListWithOptions returns checklists with the specified options.
+func (s *ChecklistService) ListWithOptions(ctx context.Context, opts ListOptions) ([]Checklist, error) {
+	path := "/checklists.json"
+	if opts.Archived {
+		path += "?archived=true"
+	}
+
+	var checklists []Checklist
+	if err := s.client.doGet(ctx, path, &checklists); err != nil {
+		return nil, err
+	}
+	return checklists, nil
+}
+
+// Get returns a single checklist by ID.
+func (s *ChecklistService) Get(ctx context.Context, id int) (*Checklist, error) {
+	path := fmt.Sprintf("/checklists/%d.json", id)
+
+	var checklist Checklist
+	if err := s.client.doGet(ctx, path, &checklist); err != nil {
+		return nil, err
+	}
+	return &checklist, nil
+}
+
+// createChecklistRequest is the request body for creating a checklist.
+type createChecklistRequest struct {
+	Name string `json:"name"`
+}
+
+// Create creates a new checklist with the given name.
+func (s *ChecklistService) Create(ctx context.Context, name string) (*Checklist, error) {
+	body := createChecklistRequest{Name: name}
+
+	var checklist Checklist
+	if err := s.client.doPost(ctx, "/checklists.json", body, &checklist); err != nil {
+		return nil, err
+	}
+	return &checklist, nil
+}
+
+// updateChecklistRequest is the request body for updating a checklist.
+type updateChecklistRequest struct {
+	Name string `json:"name"`
+}
+
+// Update updates the name of an existing checklist.
+func (s *ChecklistService) Update(ctx context.Context, id int, name string) (*Checklist, error) {
+	path := fmt.Sprintf("/checklists/%d.json", id)
+	body := updateChecklistRequest{Name: name}
+
+	var checklist Checklist
+	if err := s.client.doPut(ctx, path, body, &checklist); err != nil {
+		return nil, err
+	}
+	return &checklist, nil
+}
+
+// Delete permanently deletes a checklist by ID.
+func (s *ChecklistService) Delete(ctx context.Context, id int) error {
+	path := fmt.Sprintf("/checklists/%d.json", id)
+	return s.client.doDelete(ctx, path)
+}