feat(copilot): add GitHub Enterprise Server support (#2175)

* feat(copilot): add GitHub Enterprise Server support

* fix(copilot): address GHES PR review findings (P1 + 2×P2)

- P1: Use composite account ID (domain:user_id) for GHES to prevent
  cross-instance ID collisions; github.com keeps plain numeric ID for
  backward compatibilit
- P2-a: Use get_api_endpoint() for model list URL with automatic
  fallback to static URL when dynamic endpoint resolution fails
- P2-b: Add normalize_github_domain() as backend SSOT for domain
  normalization (lowercase, strip protocol/path/query, reject userinfo)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

src/components/providers/forms/hooks/useCopilotAuth.ts

@@ -1,8 +1,8 @@
 import type { GitHubAccount } from "@/lib/api";
 import { useManagedAuth } from "./useManagedAuth";
 
-export function useCopilotAuth() {
-  const managedAuth = useManagedAuth("github_copilot");
+export function useCopilotAuth(githubDomain?: string) {
+  const managedAuth = useManagedAuth("github_copilot", githubDomain);
   const defaultAccount =
     managedAuth.accounts.find(
       (account) => account.id === managedAuth.defaultAccountId,

src/components/providers/forms/hooks/useManagedAuth.ts

@@ -10,7 +10,10 @@ import type {
 
 type PollingState = "idle" | "polling" | "success" | "error";
 
-export function useManagedAuth(authProvider: ManagedAuthProvider) {
+export function useManagedAuth(
+  authProvider: ManagedAuthProvider,
+  githubDomain?: string,
+) {
   const queryClient = useQueryClient();
   const queryKey = ["managed-auth-status", authProvider];
 
@@ -52,7 +55,7 @@ export function useManagedAuth(authProvider: ManagedAuthProvider) {
   }, [stopPolling]);
 
   const startLoginMutation = useMutation({
-    mutationFn: () => authApi.authStartLogin(authProvider),
+    mutationFn: () => authApi.authStartLogin(authProvider, githubDomain),
     onSuccess: async (response) => {
       setDeviceCode(response);
       setPollingState("polling");
@@ -87,6 +90,7 @@ export function useManagedAuth(authProvider: ManagedAuthProvider) {
           const newAccount = await authApi.authPollForAccount(
             authProvider,
             response.device_code,
+            githubDomain,
           );
           if (newAccount) {
             stopPolling();