feat: hook syncUser to login callback

Co-authored-by: Ona <no-reply@ona.com>

convex/model/user.ts

@@ -1,4 +1,6 @@
+import type { Id } from "../_generated/dataModel"
 import type { MutationCtx, QueryCtx } from "../_generated/server"
+import type { AuthenticatedMutationCtx } from "../functions"
 import * as Err from "./error"
 
 /**
@@ -36,3 +38,9 @@ export async function userOrThrow(ctx: QueryCtx | MutationCtx) {
 
 	return user
 }
+
+export async function register(ctx: AuthenticatedMutationCtx) {
+	await ctx.db.insert("users", {
+		jwtSubject: ctx.identity.subject,
+	})
+}