feat(provider): add CodeBuddy CN provider (copilot.tencent.com)

Add Tencent CodeBuddy CN (codebuddy-cn) OAuth provider with full support:
OAuth login (GET poll with state query param), token refresh, 15-model
catalog, /v2 inference endpoint, forced streaming, OpenAI-style reasoning,
and per-model capabilities. Renamed from codebuddy to codebuddy-cn to allow
a future codebuddy-ai variant.

Co-authored-by: Cursor <cursoragent@cursor.com>

open-sse/services/tokenRefresh.js

@@ -11,6 +11,7 @@ import {
   refreshIflowToken,
   refreshGitHubToken,
   refreshCopilotToken,
+  refreshCodebuddyToken,
   classifyOAuthRefreshError,
 } from "./tokenRefresh/providers.js";
 
@@ -25,6 +26,7 @@ export {
   refreshIflowToken,
   refreshGitHubToken,
   refreshCopilotToken,
+  refreshCodebuddyToken,
   classifyOAuthRefreshError,
 };
 
@@ -127,6 +129,7 @@ const REFRESH_HANDLERS = {
   github: (c, log) => refreshGitHubToken(c.refreshToken, log),
   kiro: (c, log) => refreshKiroToken(c.refreshToken, c.providerSpecificData, log),
   xai: (c, log) => refreshXaiToken(c.refreshToken, log),
+  "codebuddy-cn": (c, log) => refreshCodebuddyToken(c.refreshToken, log),
   vertex: vertexRefreshHandler,
   "vertex-partner": vertexRefreshHandler
 };