fix(api-config): use default API URL when account type is individual

When account type is not specified or set to 'individual', use the default
api.githubcopilot.com URL instead of constructing a subdomain-based URL.

This restores previous behavior where business users could work without
explicitly specifying their account type, as the default URL works for both
individual and business accounts.

Only constructs account-type-specific URLs (api.business.githubcopilot.com,
api.enterprise.githubcopilot.com) when those account types are explicitly
specified.

Author: HyunggyuJang

src/lib/api-config.ts

@@ -14,8 +14,9 @@ const USER_AGENT = `GitHubCopilotChat/${COPILOT_VERSION}`
 const API_VERSION = "2025-10-01"
 
 export const copilotBaseUrl = (state: State) =>
-  `https://api.${state.accountType}.githubcopilot.com`
-
+  state.accountType === "individual" ?
+    "https://api.githubcopilot.com"
+  : `https://api.${state.accountType}.githubcopilot.com`
 export const copilotHeaders = (state: State, vision: boolean = false) => {
   const headers: Record<string, string> = {
     Authorization: `Bearer ${state.copilotToken}`,