feat: add --no-update-check flag and disable update check via config (issue #23)

Add support for disabling the automatic update check at startup, which could cause delays on air-gapped or offline machines due to DNS timeouts.

- Add --no-update-check CLI flag for one-time override
- Add check_for_updates field (*bool) to AppConfig with default true
- CLI flag overrides the config file setting (both feed into IsUpdateCheckEnabled)
- Move update check from --version template to TUI Init() only, respecting the new configuration
- Remove getVersionWithUpdateCheck() from cmd/root.go; --version now prints a plain version string
- Rename internal/config/keybindings.go → appconfig.go and keybindings_test.go → appconfig_test.go to reflect the broader scope of the file
- Add TestIsUpdateCheckEnabled with table-driven cases (nil config, nil field, true, false) and extend existing integration test with a CheckForUpdates round-trip
- Update README: document --no-update-check flag, config option, and rename "Custom Key Bindings" section to "Application Configuration"

internal/config/appconfig.go

@@ -0,0 +1,155 @@
+package config
+
+import (
+	"encoding/json"
+	"errors"
+	"os"
+	"path/filepath"
+)
+
+// KeyBindings represents configurable key bindings for the application
+type KeyBindings struct {
+	// Quit keys - keys that will quit the application
+	QuitKeys []string `json:"quit_keys"`
+
+	// DisableEscQuit - if true, ESC key won't quit the application (useful for vim users)
+	DisableEscQuit bool `json:"disable_esc_quit"`
+}
+
+// AppConfig represents the main application configuration
+type AppConfig struct {
+	CheckForUpdates *bool       `json:"check_for_updates,omitempty"`
+	KeyBindings     KeyBindings `json:"key_bindings"`
+}
+
+// IsUpdateCheckEnabled returns true if the update check is enabled (default: true)
+func (c *AppConfig) IsUpdateCheckEnabled() bool {
+	if c == nil || c.CheckForUpdates == nil {
+		return true
+	}
+	return *c.CheckForUpdates
+}
+
+// GetDefaultKeyBindings returns the default key bindings configuration
+func GetDefaultKeyBindings() KeyBindings {
+	return KeyBindings{
+		QuitKeys:       []string{"q", "ctrl+c"}, // Default keeps current behavior minus ESC
+		DisableEscQuit: false,                   // Default to false for backward compatibility
+	}
+}
+
+// GetDefaultAppConfig returns the default application configuration
+func GetDefaultAppConfig() AppConfig {
+	return AppConfig{
+		KeyBindings: GetDefaultKeyBindings(),
+	}
+}
+
+// GetAppConfigPath returns the path to the application config file
+func GetAppConfigPath() (string, error) {
+	configDir, err := GetSSHMConfigDir()
+	if err != nil {
+		return "", err
+	}
+
+	return filepath.Join(configDir, "config.json"), nil
+}
+
+// LoadAppConfig loads the application configuration from file
+// If the file doesn't exist, it returns the default configuration
+func LoadAppConfig() (*AppConfig, error) {
+	configPath, err := GetAppConfigPath()
+	if err != nil {
+		return nil, err
+	}
+
+	// If config file doesn't exist, return default config and create the file
+	if _, err := os.Stat(configPath); os.IsNotExist(err) {
+		defaultConfig := GetDefaultAppConfig()
+
+		// Create config directory if it doesn't exist
+		configDir := filepath.Dir(configPath)
+		if err := os.MkdirAll(configDir, 0755); err != nil {
+			return nil, err
+		}
+
+		// Save default config to file
+		if err := SaveAppConfig(&defaultConfig); err != nil {
+			// If we can't save, just return the default config without erroring
+			// This allows the app to work even if config file can't be created
+			return &defaultConfig, nil
+		}
+
+		return &defaultConfig, nil
+	}
+
+	// Read existing config file
+	data, err := os.ReadFile(configPath)
+	if err != nil {
+		return nil, err
+	}
+
+	var config AppConfig
+	if err := json.Unmarshal(data, &config); err != nil {
+		return nil, err
+	}
+
+	// Validate and fill in missing fields with defaults
+	config = mergeWithDefaults(config)
+
+	return &config, nil
+}
+
+// SaveAppConfig saves the application configuration to file
+func SaveAppConfig(config *AppConfig) error {
+	if config == nil {
+		return errors.New("config cannot be nil")
+	}
+
+	configPath, err := GetAppConfigPath()
+	if err != nil {
+		return err
+	}
+
+	// Create config directory if it doesn't exist
+	configDir := filepath.Dir(configPath)
+	if err := os.MkdirAll(configDir, 0755); err != nil {
+		return err
+	}
+
+	data, err := json.MarshalIndent(config, "", "  ")
+	if err != nil {
+		return err
+	}
+
+	return os.WriteFile(configPath, data, 0644)
+}
+
+// mergeWithDefaults ensures all required fields are set with defaults if missing
+func mergeWithDefaults(config AppConfig) AppConfig {
+	defaults := GetDefaultAppConfig()
+
+	// If QuitKeys is empty, use defaults
+	if len(config.KeyBindings.QuitKeys) == 0 {
+		config.KeyBindings.QuitKeys = defaults.KeyBindings.QuitKeys
+	}
+
+	return config
+}
+
+// ShouldQuitOnKey checks if the given key should trigger quit based on configuration
+func (kb *KeyBindings) ShouldQuitOnKey(key string) bool {
+	// Special handling for ESC key
+	if key == "esc" {
+		return !kb.DisableEscQuit
+	}
+
+	// Check if key is in the quit keys list
+	for _, quitKey := range kb.QuitKeys {
+		if quitKey == key {
+			return true
+		}
+	}
+
+	return false
+}