fix(opencode): fix free tier 403 error and improve China region handling

- Force stream:true and cloak decoy tools (bash, read) for OpenCode free tier
- Support connection testing for opencode in testUtils
- Expand error message slice limits in auth and ping to preserve workspace link
- Add concise China region link chip in provider detail page

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

src/app/api/models/test/ping.js

@@ -160,7 +160,7 @@ export async function pingModelByKind(model, kind, baseUrl = `http://127.0.0.1:$
 
   if (!res.ok) {
     const detail = parsed?.error?.message || parsed?.msg || parsed?.message || parsed?.error || rawText;
-    return { ok: false, latencyMs, error: `HTTP ${res.status}${detail ? `: ${String(detail).slice(0, 240)}` : ""}`, status: res.status };
+    return { ok: false, latencyMs, error: `HTTP ${res.status}${detail ? `: ${String(detail).slice(0, 500)}` : ""}`, status: res.status };
   }
 
   const providerStatus = parsed?.status;