Add config validation, remove command, status filtering, and unlock method display

config check: validates UUID format, recognized methods, keyfile
consistency and existence. Reports all issues with alias context.

remove: deletes a device from config by alias. Inverse of add.

status: --mounted, --unlocked, --locked flags filter the device table.
Flags combine as OR.

mount/unlock: display which method succeeded and key slot used, e.g.
"(fido2, key slot 1)". cryptsetup Open now runs with -v and parses
"Key slot N unlocked" from stderr via io.MultiWriter.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cmd/unlock.go

@@ -54,6 +54,6 @@ func runUnlock(cmd *cobra.Command, args []string) error {
 		return err
 	}
 
-	fmt.Printf("Unlocked %s -> %s\n", target, result.Device.DevicePath)
+	fmt.Printf("Unlocked %s -> %s %s\n", target, result.Device.DevicePath, formatMethod(result))
 	return nil
 }