refactor(consts): extract USER_AGENT string into constant

Replace hard-coded 'stackone-ai-node' User-Agent string with a shared
constant to improve maintainability and ensure consistency across the
codebase.

Changes:
- Add USER_AGENT constant to src/consts.ts
- Update requestBuilder.ts to use USER_AGENT constant
- Update rpc-client.ts to use USER_AGENT constant
- Update utils/errors.ts to use USER_AGENT constant
- Update requestBuilder.test.ts to use USER_AGENT constant

This centralises the User-Agent value, making future updates simpler
and reducing the risk of inconsistent values across different modules.

Author: ryoppippi

src/consts.ts

@@ -1,3 +1,8 @@
+/**
+ * Package name used as User-Agent header
+ */
+export const USER_AGENT = 'stackone-ai-node';
+
 /**
  * Default base URL for StackOne API
  */

src/requestBuilder.test.ts

@@ -1,8 +1,9 @@
 import { http, HttpResponse } from 'msw';
 import { server } from '../mocks/node';
+import { USER_AGENT } from './consts';
+import { RequestBuilder } from './requestBuilder';
 import { type HttpExecuteConfig, ParameterLocation } from './types';
 import { StackOneAPIError } from './utils/errors';
-import { RequestBuilder } from './requestBuilder';
 
 describe('RequestBuilder', () => {
 	let builder: RequestBuilder;
@@ -79,7 +80,7 @@ describe('RequestBuilder', () => {
 		const headers = builder.prepareHeaders();
 
 		expect(headers).toEqual({
-			'User-Agent': 'stackone-ai-node',
+			'User-Agent': USER_AGENT,
 			'Initial-Header': 'test',
 			'Custom-Header': 'value',
 		});
@@ -170,7 +171,7 @@ describe('RequestBuilder', () => {
 			url: 'https://api.example.com/test/path-value',
 			method: 'GET',
 			headers: {
-				'User-Agent': 'stackone-ai-node',
+				'User-Agent': USER_AGENT,
 				'Initial-Header': 'test',
 			},
 			body: undefined,

src/requestBuilder.ts

@@ -1,3 +1,4 @@
+import { USER_AGENT } from './consts';
 import {
 	type ExecuteOptions,
 	type HttpBodyType,
@@ -57,7 +58,7 @@ export class RequestBuilder {
 	 */
 	prepareHeaders(): Record<string, string> {
 		return {
-			'User-Agent': 'stackone-ai-node',
+			'User-Agent': USER_AGENT,
 			...this.headers,
 		};
 	}

src/rpc-client.ts

@@ -1,3 +1,4 @@
+import { USER_AGENT } from './consts';
 import { STACKONE_HEADER_KEYS } from './headers';
 import {
 	type RpcActionRequest,
@@ -68,7 +69,7 @@ export class RpcClient {
 			const httpHeaders = {
 				'Content-Type': 'application/json',
 				Authorization: this.authHeader,
-				'User-Agent': 'stackone-ai-node',
+				'User-Agent': USER_AGENT,
 				...forwardedHeaders,
 			} satisfies Record<string, string>;
 

src/utils/errors.ts

@@ -1,4 +1,4 @@
-// Type aliases for common types
+import { USER_AGENT } from '../consts';
 
 /**
  * Base exception for StackOne errors
@@ -73,7 +73,7 @@ export class StackOneAPIError extends StackOneError {
 		// Add request headers information (for debugging)
 		errorMessage += '\n\nRequest Headers:';
 		errorMessage += '\n- Authorization: [REDACTED]';
-		errorMessage += '\n- User-Agent: stackone-ai-node';
+		errorMessage += `\n- User-Agent: ${USER_AGENT}`;
 
 		// Add request body information if available
 		if (this.requestBody) {