Implement Project API methods

Add direct client methods for project/board operations:

- GetAllProjects(ctx) - list all accessible projects
- GetProjectByID(ctx, projectID) - get project by ID
- GetProjectByName(ctx, name) - get project by name

All methods:
- Use context for cancellation support
- Return ErrProjectNotFound when project doesn't exist
- Properly wrap errors with context

Closes: kanboard-api-apl

projects.go

@@ -0,0 +1,49 @@
+package kanboard
+
+import (
+	"context"
+	"fmt"
+)
+
+// GetAllProjects returns all projects accessible to the authenticated user.
+func (c *Client) GetAllProjects(ctx context.Context) ([]Project, error) {
+	var result []Project
+	if err := c.call(ctx, "getAllProjects", nil, &result); err != nil {
+		return nil, fmt.Errorf("getAllProjects: %w", err)
+	}
+	return result, nil
+}
+
+// GetProjectByID returns a project by its ID.
+// Returns ErrProjectNotFound if the project does not exist.
+func (c *Client) GetProjectByID(ctx context.Context, projectID int) (*Project, error) {
+	params := map[string]int{"project_id": projectID}
+
+	var result *Project
+	if err := c.call(ctx, "getProjectById", params, &result); err != nil {
+		return nil, fmt.Errorf("getProjectById: %w", err)
+	}
+
+	if result == nil {
+		return nil, fmt.Errorf("%w: project %d", ErrProjectNotFound, projectID)
+	}
+
+	return result, nil
+}
+
+// GetProjectByName returns a project by its name.
+// Returns ErrProjectNotFound if the project does not exist.
+func (c *Client) GetProjectByName(ctx context.Context, name string) (*Project, error) {
+	params := map[string]string{"name": name}
+
+	var result *Project
+	if err := c.call(ctx, "getProjectByName", params, &result); err != nil {
+		return nil, fmt.Errorf("getProjectByName: %w", err)
+	}
+
+	if result == nil {
+		return nil, fmt.Errorf("%w: project %q", ErrProjectNotFound, name)
+	}
+
+	return result, nil
+}