add charjs apis for bgembed (#324)

# PR Checklist
- [x] Did you check if it works normally in all models? *ignore this
when it dosen't uses models*
- [x] Did you check if it works normally in all of web, local and node
hosted versions? if it dosen't, did you blocked it in those versions?
- [x] Did you added a type def?

# Description

It seems like someone is holding breath for this.

![output](https://github.com/kwaroran/RisuAI/assets/133192207/1da08982-8d95-4cbf-aa11-8ca3b0c8b671)

src/ts/plugins/embedscript.ts

@@ -183,6 +183,25 @@ addWorkerFunction('setCharacterFirstMessage', async (data:string) => {
     return true
 })
 
+addWorkerFunction('getBackgroundEmbedding', async () => {
+    const db = get(DataBase)
+    const selectedChar = get(selectedCharID)
+    const char = db.characters[selectedChar]
+    return char.backgroundHTML
+})
+
+addWorkerFunction('setBackgroundEmbedding', async (data:string) => {
+    const db = get(DataBase)
+    const selectedChar = get(selectedCharID)
+    if(typeof data !== 'string'){
+        return false
+    }
+    db.characters[selectedChar].backgroundHTML = data
+    setDatabase(db)
+    return true
+})
+
+
 addWorkerFunction('getState', async (statename) => {
     const db = get(DataBase)
     const selectedChar = get(selectedCharID)