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/i18n/locales/en.json

@@ -889,7 +889,11 @@
     "retry": "Retry",
     "copyCode": "Copy code",
     "migrationFailed": "Legacy auth migration failed: {{error}}",
-    "loadModelsFailed": "Failed to load Copilot models"
+    "loadModelsFailed": "Failed to load Copilot models",
+    "deploymentType": "GitHub Deployment Type",
+    "deploymentGitHubCom": "GitHub.com",
+    "deploymentEnterprise": "GitHub Enterprise Server",
+    "enterpriseDomainPlaceholder": "e.g. company.ghe.com"
   },
   "codexOauth": {
     "authStatus": "Auth status",

src/i18n/locales/ja.json

@@ -889,7 +889,11 @@
     "retry": "再試行",
     "copyCode": "コードをコピー",
     "migrationFailed": "旧認証データの移行に失敗しました: {{error}}",
-    "loadModelsFailed": "Copilot モデル一覧の読み込みに失敗しました"
+    "loadModelsFailed": "Copilot モデル一覧の読み込みに失敗しました",
+    "deploymentType": "GitHub デプロイメントタイプ",
+    "deploymentGitHubCom": "GitHub.com",
+    "deploymentEnterprise": "GitHub Enterprise Server",
+    "enterpriseDomainPlaceholder": "例: company.ghe.com"
   },
   "codexOauth": {
     "authStatus": "認証状態",

src/i18n/locales/zh.json

@@ -890,7 +890,11 @@
     "retry": "重试",
     "copyCode": "复制代码",
     "migrationFailed": "旧认证数据迁移失败：{{error}}",
-    "loadModelsFailed": "加载 Copilot 模型列表失败"
+    "loadModelsFailed": "加载 Copilot 模型列表失败",
+    "deploymentType": "GitHub 部署类型",
+    "deploymentGitHubCom": "GitHub.com",
+    "deploymentEnterprise": "GitHub Enterprise Server",
+    "enterpriseDomainPlaceholder": "例如：company.ghe.com"
   },
   "codexOauth": {
     "authStatus": "认证状态",