Complete Client struct with fluent configuration

Add full client configuration with fluent builder pattern:

- WithTimeout(duration) - configurable request timeout
- WithLogger(slog.Logger) - optional debug logging
- DefaultTimeout constant (30 seconds)
- Default HTTP client with timeout on construction

All fluent methods return same client instance for chaining.
Client is thread-safe for concurrent use.

Closes: kanboard-api-uls

client_test.go

@@ -0,0 +1,173 @@
+package kanboard
+
+import (
+	"log/slog"
+	"net/http"
+	"os"
+	"testing"
+	"time"
+)
+
+func TestNewClient(t *testing.T) {
+	client := NewClient("https://kanboard.example.com")
+
+	if client.baseURL != "https://kanboard.example.com" {
+		t.Errorf("expected baseURL='https://kanboard.example.com', got %s", client.baseURL)
+	}
+	if client.endpoint != "https://kanboard.example.com/jsonrpc.php" {
+		t.Errorf("expected endpoint='https://kanboard.example.com/jsonrpc.php', got %s", client.endpoint)
+	}
+	if client.httpClient == nil {
+		t.Error("expected httpClient to be initialized")
+	}
+	if client.httpClient.Timeout != DefaultTimeout {
+		t.Errorf("expected timeout=%v, got %v", DefaultTimeout, client.httpClient.Timeout)
+	}
+}
+
+func TestNewClient_TrailingSlash(t *testing.T) {
+	client := NewClient("https://kanboard.example.com/")
+
+	if client.baseURL != "https://kanboard.example.com" {
+		t.Errorf("trailing slash should be removed, got %s", client.baseURL)
+	}
+	if client.endpoint != "https://kanboard.example.com/jsonrpc.php" {
+		t.Errorf("expected endpoint='https://kanboard.example.com/jsonrpc.php', got %s", client.endpoint)
+	}
+}
+
+func TestNewClient_Subdirectory(t *testing.T) {
+	client := NewClient("https://example.com/kanboard")
+
+	if client.endpoint != "https://example.com/kanboard/jsonrpc.php" {
+		t.Errorf("expected endpoint='https://example.com/kanboard/jsonrpc.php', got %s", client.endpoint)
+	}
+}
+
+func TestDefaultTimeout(t *testing.T) {
+	if DefaultTimeout != 30*time.Second {
+		t.Errorf("expected DefaultTimeout=30s, got %v", DefaultTimeout)
+	}
+}
+
+func TestClient_WithAPIToken(t *testing.T) {
+	client := NewClient("https://example.com")
+	result := client.WithAPIToken("my-token")
+
+	// Should return same client instance
+	if client != result {
+		t.Error("WithAPIToken should return the same client instance")
+	}
+
+	if client.auth == nil {
+		t.Error("auth should be set")
+	}
+}
+
+func TestClient_WithBasicAuth(t *testing.T) {
+	client := NewClient("https://example.com")
+	result := client.WithBasicAuth("admin", "password")
+
+	// Should return same client instance
+	if client != result {
+		t.Error("WithBasicAuth should return the same client instance")
+	}
+
+	if client.auth == nil {
+		t.Error("auth should be set")
+	}
+}
+
+func TestClient_WithHTTPClient(t *testing.T) {
+	customClient := &http.Client{
+		Timeout: 60 * time.Second,
+	}
+
+	client := NewClient("https://example.com")
+	result := client.WithHTTPClient(customClient)
+
+	// Should return same client instance
+	if client != result {
+		t.Error("WithHTTPClient should return the same client instance")
+	}
+
+	if client.httpClient != customClient {
+		t.Error("httpClient should be set to custom client")
+	}
+}
+
+func TestClient_WithTimeout(t *testing.T) {
+	client := NewClient("https://example.com")
+	originalClient := client.httpClient
+
+	result := client.WithTimeout(60 * time.Second)
+
+	// Should return same client instance
+	if client != result {
+		t.Error("WithTimeout should return the same client instance")
+	}
+
+	// Should create new http.Client
+	if client.httpClient == originalClient {
+		t.Error("WithTimeout should create a new http.Client")
+	}
+
+	if client.httpClient.Timeout != 60*time.Second {
+		t.Errorf("expected timeout=60s, got %v", client.httpClient.Timeout)
+	}
+}
+
+func TestClient_WithLogger(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+
+	client := NewClient("https://example.com")
+	result := client.WithLogger(logger)
+
+	// Should return same client instance
+	if client != result {
+		t.Error("WithLogger should return the same client instance")
+	}
+
+	if client.logger != logger {
+		t.Error("logger should be set")
+	}
+}
+
+func TestClient_FluentChaining(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+
+	client := NewClient("https://example.com").
+		WithAPIToken("my-token").
+		WithTimeout(60 * time.Second).
+		WithLogger(logger)
+
+	if client.auth == nil {
+		t.Error("auth should be set via chaining")
+	}
+	if client.httpClient.Timeout != 60*time.Second {
+		t.Errorf("timeout should be 60s, got %v", client.httpClient.Timeout)
+	}
+	if client.logger != logger {
+		t.Error("logger should be set via chaining")
+	}
+}
+
+func TestClient_DefaultsWithoutConfiguration(t *testing.T) {
+	client := NewClient("https://example.com")
+
+	// Should have defaults
+	if client.httpClient == nil {
+		t.Error("httpClient should not be nil")
+	}
+	if client.httpClient.Timeout != DefaultTimeout {
+		t.Errorf("default timeout should be %v", DefaultTimeout)
+	}
+
+	// Should have nil for optional fields
+	if client.auth != nil {
+		t.Error("auth should be nil by default")
+	}
+	if client.logger != nil {
+		t.Error("logger should be nil by default")
+	}
+}