fix: improve GitHub Copilot integration

src/providers/github-copilot-utils.ts

@@ -0,0 +1,24 @@
+export const DEFAULT_GITHUB_COPILOT_BASE_URL = "https://api.githubcopilot.com";
+
+export function resolveGithubCopilotUserAgent(): string {
+  const version = process.env.CLAWDBOT_VERSION ?? process.env.npm_package_version ?? "unknown";
+  return `clawdbot/${version}`;
+}
+
+export function normalizeGithubCopilotDomain(input: string | null | undefined): string | null {
+  const trimmed = (input ?? "").trim();
+  if (!trimmed) return null;
+  try {
+    const url = trimmed.includes("://") ? new URL(trimmed) : new URL(`https://${trimmed}`);
+    return url.hostname;
+  } catch {
+    return null;
+  }
+}
+
+export function resolveGithubCopilotBaseUrl(enterpriseDomain?: string | null): string {
+  if (enterpriseDomain && enterpriseDomain.trim()) {
+    return `https://copilot-api.${enterpriseDomain.trim()}`;
+  }
+  return DEFAULT_GITHUB_COPILOT_BASE_URL;
+}