Refactor unlockers command structure and add quiet flag to list command

- Rename 'unlockers' command to 'unlocker' for consistency
- Move all unlocker subcommands (list, add, remove) under single 'unlocker' command
- Add --quiet/-q flag to 'secret list' for scripting support
- Update documentation and tests to reflect command changes

The quiet flag outputs only secret names without headers or formatting,
making it ideal for shell script usage like: secret get $(secret list -q | head -1)

internal/cli/root.go

@@ -35,7 +35,6 @@ func newRootCmd() *cobra.Command {
 	cmd.AddCommand(newGetCmd())
 	cmd.AddCommand(newListCmd())
 	cmd.AddCommand(newRemoveCmd())
-	cmd.AddCommand(newUnlockersCmd())
 	cmd.AddCommand(newUnlockerCmd())
 	cmd.AddCommand(newImportCmd())
 	cmd.AddCommand(newEncryptCmd())