feat: add orm-test package — M:N integration tests against real PostgreSQL

New graphql/orm-test package that exercises ORM M:N patterns against a
live PostGraphile schema via graphile-test:

- SQL fixtures: posts, tags, post_tags junction with @behavior +manyToMany
- ManyToManyOptInPreset enabled for M:N connection fields
- Tests: addTag (createPostTag), removeTag (deletePostTagByPostIdAndTagId,
  deletePostTagByRowId), CRUD, reverse M:N direction, unique constraint
- 10/10 tests pass locally

Author: pyramation

graphql/orm-test/__fixtures__/seed/schema.sql

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+-- Schema for orm-test: M:N integration tests
+-- posts <-> tags via post_tags junction table
+
+CREATE SCHEMA IF NOT EXISTS "orm_test";
+
+GRANT USAGE ON SCHEMA "orm_test" TO administrator, authenticated, anonymous;
+
+ALTER DEFAULT PRIVILEGES IN SCHEMA "orm_test"
+  GRANT ALL ON TABLES TO administrator;
+ALTER DEFAULT PRIVILEGES IN SCHEMA "orm_test"
+  GRANT USAGE ON SEQUENCES TO administrator, authenticated;
+ALTER DEFAULT PRIVILEGES IN SCHEMA "orm_test"
+  GRANT ALL ON FUNCTIONS TO administrator, authenticated, anonymous;
+
+-- =============================================================================
+-- Table: posts
+-- =============================================================================
+CREATE TABLE "orm_test".posts (
+  id uuid PRIMARY KEY DEFAULT uuid_generate_v4(),
+  title text NOT NULL,
+  body text,
+  is_published boolean DEFAULT false,
+  created_at timestamptz DEFAULT now(),
+  updated_at timestamptz DEFAULT now()
+);
+
+-- =============================================================================
+-- Table: tags
+-- =============================================================================
+CREATE TABLE "orm_test".tags (
+  id uuid PRIMARY KEY DEFAULT uuid_generate_v4(),
+  name text NOT NULL UNIQUE,
+  color text DEFAULT '#888888',
+  created_at timestamptz DEFAULT now()
+);
+
+-- =============================================================================
+-- Table: post_tags (junction)
+-- M:N relationship between posts and tags
+-- =============================================================================
+CREATE TABLE "orm_test".post_tags (
+  id uuid PRIMARY KEY DEFAULT uuid_generate_v4(),
+  post_id uuid NOT NULL REFERENCES "orm_test".posts(id) ON DELETE CASCADE,
+  tag_id uuid NOT NULL REFERENCES "orm_test".tags(id) ON DELETE CASCADE,
+  created_at timestamptz DEFAULT now(),
+  UNIQUE(post_id, tag_id)
+);
+
+CREATE INDEX post_tags_post_id_idx ON "orm_test".post_tags (post_id);
+CREATE INDEX post_tags_tag_id_idx ON "orm_test".post_tags (tag_id);
+
+-- Enable many-to-many for this junction table
+COMMENT ON TABLE "orm_test".post_tags IS E'@behavior +manyToMany';
+
+-- =============================================================================
+-- Timestamp triggers
+-- =============================================================================
+CREATE TRIGGER posts_timestamps_tg
+  BEFORE INSERT OR UPDATE ON "orm_test".posts
+  FOR EACH ROW EXECUTE PROCEDURE stamps.timestamps();
+
+-- =============================================================================
+-- Grant table permissions
+-- =============================================================================
+GRANT SELECT, INSERT, UPDATE, DELETE ON "orm_test".posts TO administrator, authenticated, anonymous;
+GRANT SELECT, INSERT, UPDATE, DELETE ON "orm_test".tags TO administrator, authenticated, anonymous;
+GRANT SELECT, INSERT, UPDATE, DELETE ON "orm_test".post_tags TO administrator, authenticated, anonymous;

graphql/orm-test/__fixtures__/seed/setup.sql

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+-- Setup for orm-test
+-- Creates required extensions and roles
+
+CREATE EXTENSION IF NOT EXISTS "uuid-ossp";
+
+DO $$
+BEGIN
+  IF NOT EXISTS (SELECT FROM pg_roles WHERE rolname = 'administrator') THEN
+    CREATE ROLE administrator;
+  END IF;
+  IF NOT EXISTS (SELECT FROM pg_roles WHERE rolname = 'authenticated') THEN
+    CREATE ROLE authenticated;
+  END IF;
+  IF NOT EXISTS (SELECT FROM pg_roles WHERE rolname = 'anonymous') THEN
+    CREATE ROLE anonymous;
+  END IF;
+END
+$$;
+
+CREATE SCHEMA IF NOT EXISTS stamps;
+
+CREATE OR REPLACE FUNCTION stamps.timestamps()
+RETURNS TRIGGER AS $$
+BEGIN
+  IF TG_OP = 'INSERT' THEN
+    NEW.created_at = COALESCE(NEW.created_at, now());
+  END IF;
+  NEW.updated_at = now();
+  RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;

graphql/orm-test/__fixtures__/seed/test-data.sql

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+-- Seed data for orm-test
+
+INSERT INTO "orm_test".posts (id, title, body, is_published)
+VALUES
+  ('11111111-1111-1111-1111-111111111111', 'Hello World', 'First post content', true),
+  ('22222222-2222-2222-2222-222222222222', 'Second Post', 'Another post', false);
+
+INSERT INTO "orm_test".tags (id, name, color)
+VALUES
+  ('aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa', 'Technology', '#3B82F6'),
+  ('bbbbbbbb-bbbb-bbbb-bbbb-bbbbbbbbbbbb', 'Design', '#EC4899'),
+  ('cccccccc-cccc-cccc-cccc-cccccccccccc', 'Science', '#10B981');
+
+-- Seed one existing junction row: post1 <-> Technology
+INSERT INTO "orm_test".post_tags (post_id, tag_id)
+VALUES
+  ('11111111-1111-1111-1111-111111111111', 'aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa');