Add Filter builder, Archive/Unarchive, WithRepeat, and GoDoc examples

- Implement client-side Filter builder with tag, status, due date, and search filters
- Add unit tests for Filter with performance benchmark
- Add Archive/Unarchive methods to ChecklistService
- Add WithRepeat method to TaskBuilder for recurring tasks
- Create GoDoc examples for all major functionality

example_test.go

@@ -0,0 +1,163 @@
+package checkvist_test
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"code.beautifulmachines.dev/jakoubek/checkvist-api"
+)
+
+// This file contains GoDoc examples that appear in the package documentation.
+// All examples are runnable but require valid credentials to actually work.
+
+func Example_basicUsage() {
+	// Create a new client with your credentials
+	client := checkvist.NewClient("user@example.com", "your-api-key")
+
+	// List all checklists
+	ctx := context.Background()
+	checklists, err := client.Checklists().List(ctx)
+	if err != nil {
+		fmt.Println("Error:", err)
+		return
+	}
+
+	for _, cl := range checklists {
+		fmt.Printf("Checklist: %s (%d tasks)\n", cl.Name, cl.TaskCount)
+	}
+}
+
+func ExampleNewClient() {
+	// Basic client creation
+	client := checkvist.NewClient("user@example.com", "your-api-key")
+	_ = client
+
+	// With custom options
+	client = checkvist.NewClient("user@example.com", "your-api-key",
+		checkvist.WithTimeout(60*time.Second),
+		checkvist.WithRetryConfig(checkvist.RetryConfig{
+			MaxRetries: 5,
+			BaseDelay:  500 * time.Millisecond,
+			MaxDelay:   30 * time.Second,
+		}),
+	)
+	_ = client
+}
+
+func ExampleClient_Authenticate() {
+	client := checkvist.NewClient("user@example.com", "your-api-key")
+
+	// Explicit authentication (usually not needed - auto-authenticates on first request)
+	ctx := context.Background()
+	err := client.Authenticate(ctx)
+	if err != nil {
+		fmt.Println("Authentication failed:", err)
+		return
+	}
+	fmt.Println("Authenticated successfully")
+}
+
+func ExampleChecklistService_List() {
+	client := checkvist.NewClient("user@example.com", "your-api-key")
+	ctx := context.Background()
+
+	// List all active checklists
+	checklists, err := client.Checklists().List(ctx)
+	if err != nil {
+		fmt.Println("Error:", err)
+		return
+	}
+
+	for _, cl := range checklists {
+		fmt.Printf("- %s (ID: %d)\n", cl.Name, cl.ID)
+	}
+}
+
+func ExampleTaskService_Create() {
+	client := checkvist.NewClient("user@example.com", "your-api-key")
+	ctx := context.Background()
+
+	// Create a task using the builder pattern
+	task, err := client.Tasks(123).Create(ctx,
+		checkvist.NewTask("Buy groceries").
+			WithTags("shopping", "urgent").
+			WithDueDate(checkvist.DueTomorrow).
+			WithPriority(1),
+	)
+	if err != nil {
+		fmt.Println("Error:", err)
+		return
+	}
+	fmt.Printf("Created task: %s (ID: %d)\n", task.Content, task.ID)
+}
+
+func ExampleNewTask() {
+	// Simple task
+	task := checkvist.NewTask("Complete project report")
+
+	// Task with all options
+	task = checkvist.NewTask("Review pull request").
+		WithTags("code-review", "urgent").
+		WithDueDate(checkvist.DueTomorrow).
+		WithPriority(1).
+		WithParent(456). // Makes this a subtask
+		WithPosition(1)  // First position among siblings
+
+	_ = task
+}
+
+func ExampleNewFilter() {
+	// Assume we have a list of tasks from the API
+	tasks := []checkvist.Task{
+		{ID: 1, Content: "Buy groceries", TagsAsText: "shopping", Status: checkvist.StatusOpen},
+		{ID: 2, Content: "Call doctor", TagsAsText: "health", Status: checkvist.StatusClosed},
+		{ID: 3, Content: "Review PR", TagsAsText: "work, urgent", Status: checkvist.StatusOpen},
+	}
+
+	// Filter to open tasks with "urgent" tag
+	filtered := checkvist.NewFilter(tasks).
+		WithTag("urgent").
+		WithStatus(checkvist.StatusOpen).
+		Apply()
+
+	fmt.Printf("Found %d matching tasks\n", len(filtered))
+	// Output: Found 1 matching tasks
+}
+
+func ExampleFilter_Apply() {
+	// Create sample tasks with due dates
+	yesterday := time.Now().AddDate(0, 0, -1)
+	tomorrow := time.Now().AddDate(0, 0, 1)
+
+	tasks := []checkvist.Task{
+		{ID: 1, Content: "Overdue task", DueDate: &yesterday, Status: checkvist.StatusOpen},
+		{ID: 2, Content: "Future task", DueDate: &tomorrow, Status: checkvist.StatusOpen},
+		{ID: 3, Content: "Closed task", DueDate: &yesterday, Status: checkvist.StatusClosed},
+	}
+
+	// Find overdue open tasks
+	overdue := checkvist.NewFilter(tasks).
+		WithOverdue().
+		Apply()
+
+	for _, t := range overdue {
+		fmt.Printf("Overdue: %s\n", t.Content)
+	}
+	// Output: Overdue: Overdue task
+}
+
+func ExampleDueAt() {
+	// Set due date to a specific date
+	deadline := time.Date(2026, 3, 15, 0, 0, 0, 0, time.UTC)
+	task := checkvist.NewTask("Project deadline").
+		WithDueDate(checkvist.DueAt(deadline))
+	_ = task
+}
+
+func ExampleDueInDays() {
+	// Set due date to 7 days from now
+	task := checkvist.NewTask("Follow up").
+		WithDueDate(checkvist.DueInDays(7))
+	_ = task
+}