Add unique ID per post and an index to the db for that

src/db.ts

@@ -36,6 +36,7 @@ export function openDatabase(userID:string): Promise<IDBDatabase> {
             if (!db.objectStoreNames.contains(storeName)) {
                 let store = db.createObjectStore(storeName, { keyPath: "id", autoIncrement: true });
                 store.createIndex("datetimeIndex", "post_timestamp", { unique: false });
+                store.createIndex("postIDIndex", "data.post_id", { unique: true });
 
             }
         };