Enhancement: Empty config

When user starts kportal for the first time, and there is no config file,
kportal should create an empty config file with default values and empty
forwarding rules, so that user can easily edit the config file and add their
own rules.

internal/config/config.go

@@ -2,6 +2,7 @@ package config
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"os"
 	"strings"
@@ -10,6 +11,9 @@ import (
 	"gopkg.in/yaml.v3"
 )
 
+// ErrConfigNotFound is returned when the configuration file does not exist
+var ErrConfigNotFound = fmt.Errorf("config file not found")
+
 const (
 	// maxConfigSize is the maximum allowed configuration file size (10MB)
 	maxConfigSize = 10 * 1024 * 1024
@@ -282,6 +286,9 @@ func LoadConfig(path string) (*Config, error) {
 	// Validate file size before reading
 	fileInfo, err := os.Stat(path)
 	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			return nil, ErrConfigNotFound
+		}
 		return nil, fmt.Errorf("failed to stat config file: %w", err)
 	}
 
@@ -337,3 +344,58 @@ func (c *Config) GetAllForwards() []Forward {
 
 	return forwards
 }
+
+// NewEmptyConfig returns a minimal empty configuration with no forwards.
+// This is used when creating a new config file for the first time.
+func NewEmptyConfig() *Config {
+	return &Config{
+		Contexts: []Context{},
+	}
+}
+
+// IsEmpty returns true if the configuration has no forwards defined.
+func (c *Config) IsEmpty() bool {
+	return len(c.Contexts) == 0 || len(c.GetAllForwards()) == 0
+}
+
+// CreateEmptyConfigFile creates a new empty configuration file at the given path.
+// Returns an error if the file already exists or cannot be created.
+func CreateEmptyConfigFile(path string) error {
+	// Check if file already exists
+	if _, err := os.Stat(path); err == nil {
+		return fmt.Errorf("config file already exists: %s", path)
+	} else if !errors.Is(err, os.ErrNotExist) {
+		return fmt.Errorf("failed to check config file: %w", err)
+	}
+
+	cfg := NewEmptyConfig()
+	data, err := yaml.Marshal(cfg)
+	if err != nil {
+		return fmt.Errorf("failed to marshal empty config: %w", err)
+	}
+
+	// Add a helpful comment header
+	header := `# kportal configuration file
+# Add port forwards using the 'n' key in the TUI, or manually add them below.
+#
+# Example forward:
+#   contexts:
+#     - name: my-cluster
+#       namespaces:
+#         - name: default
+#           forwards:
+#             - resource: service/my-service
+#               protocol: tcp
+#               port: 8080
+#               localPort: 8080
+#
+`
+	content := header + string(data)
+
+	// Write with restrictive permissions (0600)
+	if err := os.WriteFile(path, []byte(content), 0600); err != nil {
+		return fmt.Errorf("failed to write config file: %w", err)
+	}
+
+	return nil
+}