docs: add AmazonQ.md knowledge base file (#50)

This PR adds the AmazonQ.md knowledge base file that contains important
information about the project structure, coding conventions, and best
practices.

The file provides:
- Project overview and architecture details
- Directory structure explanations
- Technology stack information
- Commonly used commands
- Development workflow
- Best practices for working with the codebase

This will help Amazon Q understand the repository better when assisting
with development tasks.

---------

Co-authored-by: remote-swe-app[bot] <123456+remote-swe-app[bot]@users.noreply.github.com>
Co-authored-by: Masashi Tomooka <tmokmss@users.noreply.github.com>

Author: 3 people

AmazonQ.md

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+# Serverless Full Stack WebApp Starter Kit Knowledge Base
+
+This file provides important information about the Serverless Full Stack WebApp Starter Kit repository. AI agent references this to support its work on this project.
+
+## Project Overview
+
+This project is a full stack webapp starter kit leveraging AWS serverless services, featuring:
+
+- Next.js App Router on AWS Lambda
+- CloudFront + Lambda function URL with response stream support
+- End-to-end type safety (client to server)
+- Cognito authentication
+- Real-time notifications
+- Asynchronous job queue
+- Instant deployment via AWS CDK
+
+## Project Structure
+
+The project consists of two main components:
+
+1. **WebApp** - `/webapp` directory
+   - Next.js application with App Router
+   - Frontend UI and server components
+   - Server actions
+   - TypeScript + React
+   - Tailwind CSS for styling
+
+2. **CDK (AWS Cloud Development Kit)** - `/cdk` directory
+   - Infrastructure as Code definitions
+   - AWS resource provisioning
+   - Deployment configurations
+
+### WebApp Structure
+
+```
+/webapp/src/
+├── app/
+│   ├── (root)/ 
+│   │   ├── components/ (feature-specific components)
+│   │   ├── actions.ts (server actions)
+│   │   ├── schemas.ts (validation schemas)
+│   │   └── page.tsx (main page)
+│   ├── api/
+│   ├── auth-callback/
+│   └── sign-in/
+├── components/ (shared components)
+├── hooks/
+├── jobs/
+├── lib/
+└── middleware.ts
+```
+
+## Technology Stack
+
+- **Frontend**: React, Next.js, Tailwind CSS
+- **Backend**: Next.js App Router, Server Actions, AWS Lambda
+- **Database**: Amazon Aurora PostgreSQL Serverless v2 with Prisma ORM
+- **Authentication**: Amazon Cognito
+- **Real-time**: AWS AppSync Events
+- **Infrastructure**: AWS CDK, CloudFront, Lambda, EventBridge
+
+## Coding Conventions
+
+- Use TypeScript for type safety
+- Feature-based directory structure
+- Function components with hooks for React
+- Server actions for backend logic
+- Zod for data validation
+- Prisma for database interactions
+
+## Commonly Used Commands
+
+### WebApp
+
+```bash
+# Development server (with Turbopack)
+cd webapp && npm run dev
+
+# Build the web application
+cd webapp && npm run build
+
+# Formatting
+cd webapp && npm run format
+
+# Check formatting
+cd webapp && npm run format:check
+
+# Linting
+cd webapp && npm run lint
+```
+
+### CDK
+
+```bash
+# Build the CDK project
+cd cdk && npm run build
+
+# Deploy the application to AWS
+cd cdk && npm run cdk deploy
+
+# Check for changes in the infrastructure
+cd cdk && npm run cdk diff
+```
+
+## Development Flow
+
+1. Create a branch for a new feature or bug fix
+2. Implement changes and test locally
+3. Run format and lint checks
+4. Create a PR with title and description in English and ensure CI passes
+5. Request review when the PR is ready
+
+## Best Practices
+
+1. **Directory Organization**:
+   - Group feature-specific components, actions, and schemas in the same directory
+   - Keep shared components in the top-level components directory
+
+2. **Code Quality**:
+   - Use TypeScript for type safety
+   - Validate inputs with Zod schemas
+   - Follow Next.js server/client component patterns
+
+3. **Authentication**:
+   - Use the built-in auth mechanisms for protected routes
+   - Follow Cognito authentication patterns
+
+4. **Database Access**:
+   - Use Prisma for database operations
+   - Keep database logic in server actions
+
+## Troubleshooting
+
+- **Next.js Errors**: Ensure proper separation of client/server components
+- **CDK Deployment Issues**: Check AWS credentials and permissions
+- **Authentication Problems**: Verify Cognito user pool configuration
+- **Database Connection Errors**: Check Prisma schema and connection string