Add better-auth integration and update dependencies in package.json and bun.lock

packages/backend/convex/schema.ts

@@ -1,7 +1,9 @@
 import { defineSchema, defineTable } from "convex/server";
 import { v } from "convex/values";
+import { tables } from "./betterAuth/schema";
 
 export default defineSchema({
+  ...tables,
   todos: defineTable({
     text: v.string(),
     completed: v.boolean(),