add dummy payment app to monorepo

apps/dummy-payment/.env.example

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+# Local development variables. When developped locally with Saleor inside docker, these can be set to:
+#
+# APP_IFRAME_BASE_URL = http://localhost:3000, so Dashboard on host can access iframe
+# APP_API_BASE_URL=http://host.docker.internal:3000 - so Saleor can reach App running on host, from the container.
+#
+# If developped with tunnels, set this empty, it will fallback to address the app is reached from (default port 3000).
+APP_IFRAME_BASE_URL=
+APP_API_BASE_URL=
+
+
+# Dynamodb apl
+
+AWS_ACCESS_KEY_ID=
+AWS_SECRET_ACCESS_KEY=
+AWS_REGION=
+DYNAMODB_MAIN_TABLE_NAME=
+
+# optional
+# DYNAMODB_MAIN_TABLE_TIMEOUT_MS=
+# DYNAMODB_MAIN_TABLE_CONNECTION_TIMEOUT_MS=

apps/dummy-payment/.eslintrc

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+{
+  "extends": ["next", "prettier"]
+}

apps/dummy-payment/.gitallowed

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+AGENTS.md

apps/dummy-payment/.gitignore

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+# See https://help.github.com/articles/ignoring-files/ for more about ignoring files.
+
+# dependencies
+/node_modules
+/.pnp
+.pnp.js
+
+# testing
+/coverage
+
+# next.js
+/.next/
+/out/
+
+# production
+/build
+
+# misc
+.DS_Store
+*.pem
+
+# debug
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+.pnpm-debug.log*
+
+# local env files
+.env*.local
+.envfile
+.saleor-app-auth.json
+
+# vercel
+.vercel
+
+# typescript
+*.tsbuildinfo
+
+.auth_token
+
+#editor
+.vscode
+.idea
+
+# Sentry
+.sentryclirc
+
+.env

apps/dummy-payment/.graphqlrc.yml

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+schema: graphql/schema.graphql
+documents: [graphql/**/*.graphql, src/**/*.ts, src/**/*.tsx]
+extensions:
+  codegen:
+    overwrite: true
+    generates:
+      generated/graphql.ts:
+        config:
+          dedupeFragments: true
+        plugins:
+          - typescript
+          - typescript-operations
+          - urql-introspection
+          - typescript-urql:
+              documentVariablePrefix: "Untyped"
+              fragmentVariablePrefix: "Untyped"
+          - typed-document-node
+      generated/schema.graphql:
+        plugins:
+          - schema-ast

apps/dummy-payment/.npmrc

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+strict-peer-dependencies=false
+auto-install-peers=true
+save-exact=true

apps/dummy-payment/.prettierignore

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+.next
+saleor/api.tsx
+pnpm-lock.yaml
+graphql/schema.graphql
+generated

apps/dummy-payment/.prettierrc

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+{
+  "singleQuote": false,
+  "printWidth": 100
+}

apps/dummy-payment/AGENTS.md

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+# Saleor Dummy Payment App
+
+This file provides guidance to coding agents when working with code in this repository.
+
+## Project Overview
+
+This is a Saleor Payment App that implements a dummy payment gateway for testing Saleor's Transactions API. It allows testing payment flows without a real payment provider.
+
+## Development Commands
+
+### Setup
+```bash
+pnpm install  # Install dependencies
+```
+
+### Development
+```bash
+pnpm dev      # Start dev server with codegen and Node.js inspector on port 3000
+pnpm build    # Build for production (runs codegen first)
+pnpm start    # Start production server
+```
+
+### Code Quality
+```bash
+pnpm lint     # Run ESLint
+pnpm test     # Run tests with Vitest
+```
+
+### GraphQL
+```bash
+pnpm generate      # Generate TypeScript types from GraphQL schema and operations
+pnpm fetch-schema  # Fetch latest Saleor GraphQL schema (version in package.json)
+```
+
+GraphQL operations are defined in `graphql/` directory (mutations, queries, fragments, subscriptions). The codegen generates types in `generated/graphql.ts` using urql and typed-document-node.
+
+## Architecture
+
+### Framework & Stack
+- **Next.js** with Pages Router (not App Router)
+- **tRPC** for type-safe API routes (server & client communication)
+- **urql** for GraphQL client with auth exchange
+- **Saleor App SDK** for webhook handling and APL (Auth Persistence Layer)
+- **Vitest** for testing with jsdom environment
+- **OpenTelemetry** for observability (traces & logs)
+- **Sentry** for error tracking
+
+### Key Architectural Components
+
+#### APL (Auth Persistence Layer)
+Authentication data storage configured in `src/saleor-app.ts`. Supports:
+- `FileAPL` (default) - stores auth in `.auth-data.json`
+- `UpstashAPL` - for multi-tenant deployments
+- `SaleorCloudAPL` - for Saleor Cloud deployments
+
+#### Webhook System
+All webhooks are in `src/pages/api/webhooks/`. Each webhook:
+- Uses `SaleorSyncWebhook` from `@saleor/app-sdk`
+- Wrapped with `wrapWithLoggerContext` and `withOtel` for observability
+- Has `bodyParser: false` in config for signature verification
+- Validates incoming data with Zod schemas from `src/modules/validation/`
+
+Supported webhooks:
+- `PAYMENT_GATEWAY_INITIALIZE_SESSION`
+- `TRANSACTION_INITIALIZE_SESSION`
+- `TRANSACTION_PROCESS_SESSION`
+- `TRANSACTION_REFUND_REQUESTED`
+- `TRANSACTION_CHARGE_REQUESTED`
+- `TRANSACTION_CANCELATION_REQUESTED`
+
+#### tRPC Setup
+- Server router in `src/server/routers/app-router.ts`
+- Context defined in `src/pages/api/trpc/[trpc].ts`
+- Client setup in `src/trpc-client.ts`
+- Procedures can use `procedureWithGraphqlClient` middleware for Saleor API access
+
+#### GraphQL Client
+Created via `createClient` in `src/lib/create-graphql-client.ts`:
+- Uses urql with auth exchange
+- Custom `Authorization-Bearer` header (note: not standard `Authorization: Bearer`)
+- Auth token provided via APL
+
+#### URL Generation
+`AppUrlGenerator` in `src/modules/url/app-url-generator.ts` handles:
+- External URLs for webhooks (`APP_API_BASE_URL` env var)
+- Iframe URLs for dashboard (`APP_IFRAME_BASE_URL` env var)
+- Falls back to request host if env vars not set
+- Env vars are used for local development with local Saleor instance, tunneling works without setting env vars
+
+#### Transaction Logic
+- `transaction-actions.ts` - determines available actions based on event type
+- `transaction-psp-finder.ts` - finds PSP reference from transaction events
+- `transaction-refund-checker.ts` - validates refund requests
+- Response schema validation in `src/modules/validation/sync-transaction.ts`
+
+#### Observability
+- Logger with multiple transports (console, Sentry, Vercel) in `src/lib/logger/`
+- OpenTelemetry setup in `src/lib/otel/` with traces and logs
+- Request context propagation via `logger-context.ts`
+
+### Pages Structure
+- `/` - Landing page
+- `/app/` - Dashboard pages (must be opened in Saleor Dashboard iframe context):
+  - `/app/index.tsx` - Main app page
+  - `/app/configuration.tsx` - App configuration
+  - `/app/checkout.tsx` - Checkout testing UI
+  - `/app/transactions/` - Transaction list and details
+
+### Environment Variables
+Optional for local development (defaults work without Docker):
+- `APP_IFRAME_BASE_URL` - Base URL for iframe (e.g., `http://localhost:3000`)
+- `APP_API_BASE_URL` - Base URL for webhooks (e.g., `http://host.docker.internal:3000` for Docker)
+- `APL` - Auth persistence layer type: `file` (default), `upstash`, `saleor-cloud`
+- APL-specific vars: `FILE_APL_PATH`, `UPSTASH_URL`, `UPSTASH_TOKEN`, `REST_APL_TOKEN`, `REST_APL_ENDPOINT`
+
+## Testing Payment Flows
+
+The app accepts `data` field in `transactionInitialize` and `transactionProcess` mutations to control behavior:
+
+```json
+{
+  "data": {
+    "event": {
+      "type": "CHARGE_SUCCESS",  // See TransactionEventTypeEnum
+      "includePspReference": true
+    }
+  }
+}
+```
+
+Valid event types: `CHARGE_SUCCESS`, `CHARGE_FAILURE`, `CHARGE_REQUEST`, `CHARGE_ACTION_REQUIRED`, `AUTHORIZATION_SUCCESS`, `AUTHORIZATION_FAILURE`, `AUTHORIZATION_REQUEST`, `AUTHORIZATION_ACTION_REQUIRED`
+
+Response includes:
+- `pspReference` - UUID v7 (if `includePspReference: true`)
+- `result` - mirrors the input `type`
+- `actions` - available transaction actions (determined by event type)
+- `externalUrl` - link to transaction details page in app
+- `message` - success or error message
+
+For more details check Saleor GraphQL schema and docs: docs.saleor.io
+
+## Important Notes
+
+- All webhook handlers must have `bodyParser: false` for signature verification
+- GraphQL schema version is pinned to Saleor 3.19 (see `package.json`)
+- Node version: 18.17.0 - 20.x required
+- Uses ES modules (`"type": "module"` in package.json)
+- Transaction external URLs link back to app UI for status updates