Add type of this_chid

public/script.js

@@ -553,6 +553,10 @@ let generatedPromptCache = '';
 let generation_started = new Date();
 /** @type {import('./scripts/char-data.js').v1CharData[]} */
 export let characters = [];
+/**
+ * Stringified index of a currently chosen entity in the characters array.
+ * @type {string|undefined} Yes, we hate it as much as you do.
+ */
 export let this_chid;
 let saveCharactersPage = 0;
 export const default_avatar = 'img/ai4.png';