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/sse/services/auth.js

@@ -263,7 +263,7 @@ export async function markAccountUnavailable(connectionId, status, errorText, pr
   }
   if (!shouldFallback) return { shouldFallback: false, cooldownMs: 0 };
 
-  const reason = typeof errorText === "string" ? errorText.slice(0, 100) : "Provider error";
+  const reason = typeof errorText === "string" ? errorText.slice(0, 200) : "Provider error";
   const lockUpdate = buildModelLockUpdate(githubResetAtMs ? null : model, cooldownMs);
 
   await updateProviderConnection(connectionId, {