♻️ refactor: rewrite OAuth provision business logic for new user schema

prisma/migrations/20260528142420_add_expires_in_session/migration.sql

@@ -0,0 +1,8 @@
+/*
+  Warnings:
+
+  - Added the required column `valid_until` to the `user_sessions` table without a default value. This is not possible if the table is not empty.
+
+*/
+-- AlterTable
+ALTER TABLE "user_sessions" ADD COLUMN     "valid_until" TIMESTAMPTZ NOT NULL;