refactor: migrate authentication from Supabase to Better Auth and update Prisma schema models

apps/backend/prisma/migrations/20260416194944_add_complex_user/migration.sql

@@ -0,0 +1,18 @@
+-- CreateTable
+CREATE TABLE "complex_users" (
+    "complex_id" UUID NOT NULL,
+    "user_id" TEXT NOT NULL,
+    "role" "ComplexUserRole" NOT NULL DEFAULT 'ADMIN',
+    "created_at" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "complex_users_pkey" PRIMARY KEY ("complex_id","user_id")
+);
+
+-- CreateIndex
+CREATE INDEX "complex_users_user_id_idx" ON "complex_users"("user_id");
+
+-- AddForeignKey
+ALTER TABLE "complex_users" ADD CONSTRAINT "complex_users_complex_id_fkey" FOREIGN KEY ("complex_id") REFERENCES "complexes"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "complex_users" ADD CONSTRAINT "complex_users_user_id_fkey" FOREIGN KEY ("user_id") REFERENCES "users"("id") ON DELETE CASCADE ON UPDATE CASCADE;