feat: add GetColorList for available task colors

Adds GetColorList() to query the available task colors from the
Kanboard instance. Returns a map of color_id to display name
(e.g., "yellow" -> "Yellow").

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

application_test.go

@@ -0,0 +1,94 @@
+package kanboard
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestClient_GetColorList(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		var req JSONRPCRequest
+		json.NewDecoder(r.Body).Decode(&req)
+
+		if req.Method != "getColorList" {
+			t.Errorf("expected method=getColorList, got %s", req.Method)
+		}
+
+		resp := JSONRPCResponse{
+			JSONRPC: "2.0",
+			ID:      req.ID,
+			Result: json.RawMessage(`{
+				"yellow": "Yellow",
+				"blue": "Blue",
+				"green": "Green",
+				"purple": "Purple",
+				"red": "Red",
+				"orange": "Orange",
+				"grey": "Grey",
+				"brown": "Brown",
+				"deep_orange": "Deep Orange",
+				"dark_grey": "Dark Grey",
+				"pink": "Pink",
+				"teal": "Teal",
+				"cyan": "Cyan",
+				"lime": "Lime",
+				"light_green": "Light Green",
+				"amber": "Amber"
+			}`),
+		}
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer server.Close()
+
+	client := NewClient(server.URL).WithAPIToken("test-token")
+
+	colors, err := client.GetColorList(context.Background())
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	// Check that we got some colors
+	if len(colors) != 16 {
+		t.Errorf("expected 16 colors, got %d", len(colors))
+	}
+
+	// Check specific colors
+	if colors["yellow"] != "Yellow" {
+		t.Errorf("expected yellow='Yellow', got %s", colors["yellow"])
+	}
+	if colors["blue"] != "Blue" {
+		t.Errorf("expected blue='Blue', got %s", colors["blue"])
+	}
+	if colors["deep_orange"] != "Deep Orange" {
+		t.Errorf("expected deep_orange='Deep Orange', got %s", colors["deep_orange"])
+	}
+}
+
+func TestClient_GetColorList_Empty(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		var req JSONRPCRequest
+		json.NewDecoder(r.Body).Decode(&req)
+
+		resp := JSONRPCResponse{
+			JSONRPC: "2.0",
+			ID:      req.ID,
+			Result:  json.RawMessage(`{}`),
+		}
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer server.Close()
+
+	client := NewClient(server.URL).WithAPIToken("test-token")
+
+	colors, err := client.GetColorList(context.Background())
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if len(colors) != 0 {
+		t.Errorf("expected 0 colors, got %d", len(colors))
+	}
+}