feat: add local signup and Kakao verification gate

packages/infra/prisma/gateway-migrations/20260726000000_add_local_signup_verification/migration.sql

@@ -0,0 +1,26 @@
+ALTER TABLE "app_user"
+    ADD COLUMN "terms_accepted_at" TIMESTAMP(3),
+    ADD COLUMN "privacy_accepted_at" TIMESTAMP(3),
+    ADD COLUMN "kakao_verified_at" TIMESTAMP(3),
+    ADD COLUMN "kakao_grace_started_at" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP;
+
+UPDATE "app_user"
+SET "kakao_verified_at" = COALESCE("updated_at", "created_at")
+WHERE "oauth_type" = 'KAKAO'
+  AND "kakao_verified_at" IS NULL;
+
+DO $$
+BEGIN
+    IF EXISTS (
+        SELECT 1
+        FROM "app_user"
+        GROUP BY "display_name"
+        HAVING COUNT(*) > 1
+    ) THEN
+        RAISE EXCEPTION
+            'Cannot enforce unique app_user.display_name: resolve duplicate display names before applying this migration.';
+    END IF;
+END
+$$;
+
+CREATE UNIQUE INDEX "app_user_display_name_key" ON "app_user"("display_name");