feat: switch avatar imager to epicnabbo.nl with figure conversion

- Update imager to use epicnabbo.nl by default with effect=14 and img_format=apng
- Add figure string converter (old Habbo format -> epicnabbo.nl short format)
- Update avatarImageUrl to auto-convert figure strings
- Update online-users-widget to use new avatarImageUrl
- Add tests for imager and figure conversion

src/types/admin.ts

@@ -40,4 +40,8 @@ export interface AvatarOptions {
 	gesture?: string;
 	/** Action: wav, sit, lay, etc. */
 	action?: string;
+	/** Effect ID (e.g., 14 for ghost) */
+	effect?: string | number;
+	/** Image format (e.g., "png", "apng") */
+	img_format?: string;
 }