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/ui/tui.go

@@ -16,7 +16,7 @@ import (
 )
 
 // NewModel creates a new TUI model with the given SSH hosts
-func NewModel(hosts []config.SSHHost, configFile string, searchMode bool, currentVersion string) Model {
+func NewModel(hosts []config.SSHHost, configFile string, searchMode bool, currentVersion string, noUpdateCheck bool) Model {
 	// Load application configuration
 	appConfig, err := config.LoadAppConfig()
 	if err != nil {
@@ -26,6 +26,12 @@ func NewModel(hosts []config.SSHHost, configFile string, searchMode bool, curren
 		appConfig = &defaultConfig
 	}
 
+	// CLI flag overrides config file setting
+	if noUpdateCheck {
+		f := false
+		appConfig.CheckForUpdates = &f
+	}
+
 	// Initialize the history manager
 	historyManager, err := history.NewHistoryManager()
 	if err != nil {
@@ -151,8 +157,8 @@ func NewModel(hosts []config.SSHHost, configFile string, searchMode bool, curren
 }
 
 // RunInteractiveMode starts the interactive TUI interface
-func RunInteractiveMode(hosts []config.SSHHost, configFile string, searchMode bool, currentVersion string) error {
-	m := NewModel(hosts, configFile, searchMode, currentVersion)
+func RunInteractiveMode(hosts []config.SSHHost, configFile string, searchMode bool, currentVersion string, noUpdateCheck bool) error {
+	m := NewModel(hosts, configFile, searchMode, currentVersion, noUpdateCheck)
 
 	// Start the application in alt screen mode for clean output
 	p := tea.NewProgram(m, tea.WithAltScreen())