SNS client wrapper (#15)

* feat: update package version to 0.4.0-alpha.1 and add SNS client utilities

- Updated version in package.json to 0.4.0-alpha.1
- Upgraded @typescript-eslint packages to 8.50.1
- Added aws-sdk-client-mock as a dev dependency
- Updated AWS SDK dependencies to version 3.957.0
- Introduced sns-client.ts with functions to initialize, get, reset SNS client and publish messages
- Added tests for SNS client functionalities in sns-client.test.ts
- Exported SNS client utilities from index.ts

* feat: add SNS client utilities and update documentation

Author: mwarman

README.md

@@ -94,7 +94,7 @@ export const handler = async (event: APIGatewayProxyEvent) => {
 - **📝 Structured Logging** – Pino logger pre-configured for Lambda with automatic AWS request context enrichment
 - **📤 API Response Helpers** – Standard response formatting for API Gateway with proper HTTP status codes
 - **⚙️ Configuration Validation** – Environment variable validation with Zod schema support
-- **🔌 AWS SDK Clients** – Pre-configured AWS SDK v3 clients including DynamoDB with document client support
+- **🔌 AWS SDK Clients** – Pre-configured AWS SDK v3 clients including DynamoDB and SNS with singleton patterns
 - **🔒 Full TypeScript Support** – Complete type definitions and IDE autocomplete
 - **⚡ Lambda Optimized** – Designed for performance in serverless environments
 
@@ -107,7 +107,8 @@ Comprehensive guides and examples are available in the `docs` directory:
 | **[Configuration Guide](./docs/CONFIGURATION.md)**           | Validate environment variables with Zod schemas and type safety        |
 | **[Logging Guide](./docs/LOGGING.md)**                       | Configure and use structured logging with automatic AWS Lambda context |
 | **[API Gateway Responses](./docs/API_GATEWAY_RESPONSES.md)** | Format responses for API Gateway with standard HTTP patterns           |
-| **[DynamoDB Client](./docs/DYNAMODB_CLIENT.md)**             | Use pre-configured AWS SDK v3 clients in your handlers                 |
+| **[DynamoDB Client](./docs/DYNAMODB_CLIENT.md)**             | Use pre-configured DynamoDB clients with singleton pattern             |
+| **[SNS Client](./docs/SNS_CLIENT.md)**                       | Publish messages to SNS topics with message attributes                 |
 
 ## Usage
 
@@ -195,6 +196,33 @@ export const handler = async (event: any, context: any) => {
 
 **→ See [DynamoDB Client Guide](./docs/DYNAMODB_CLIENT.md) for detailed configuration and examples**
 
+#### SNS Client
+
+Publish messages to SNS topics with optional message attributes:
+
+```typescript
+import { publishToTopic, SNSMessageAttributes } from '@leanstacks/lambda-utils';
+
+export const handler = async (event: any) => {
+  const attributes: SNSMessageAttributes = {
+    priority: {
+      DataType: 'String',
+      StringValue: 'high',
+    },
+  };
+
+  const messageId = await publishToTopic(
+    'arn:aws:sns:us-east-1:123456789012:MyTopic',
+    { orderId: '12345', status: 'completed' },
+    attributes,
+  );
+
+  return { statusCode: 200, body: JSON.stringify({ messageId }) };
+};
+```
+
+**→ See [SNS Client Guide](./docs/SNS_CLIENT.md) for detailed configuration and examples**
+
 Additional AWS Clients are coming soon.
 
 ## Examples

docs/README.md

@@ -12,13 +12,14 @@ Lambda Utilities is a collection of pre-configured tools and helpers designed to
 - **[Logging Guide](./LOGGING.md)** – Implement structured logging in your Lambda functions with Pino and automatic AWS context enrichment
 - **[API Gateway Responses](./API_GATEWAY_RESPONSES.md)** – Format Lambda responses for API Gateway with standard HTTP status codes and headers
 - **[DynamoDB Client](./DYNAMODB_CLIENT.md)** – Reusable singleton DynamoDB client instances with custom configuration
+- **[SNS Client](./SNS_CLIENT.md)** – Reusable singleton SNS client for publishing messages to topics with message attributes
 
 ## Features
 
 - 📝 **Structured Logging** – Pino logger pre-configured for Lambda with automatic request context
 - 📤 **API Response Helpers** – Standard response formatting for API Gateway integration
 - ⚙️ **Configuration Validation** – Environment variable validation with Zod schema support
-- 🔌 **AWS Clients** – Pre-configured AWS SDK v3 clients for common services
+- 🔌 **AWS Clients** – Pre-configured AWS SDK v3 clients for DynamoDB and SNS
 - 🔒 **Type Safe** – Full TypeScript support with comprehensive type definitions
 
 ## Support