Fix: import error in sandbox provider (#13971)

### What problem does this PR solve?

Fix import error in sandbox provider.

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)


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## Summary by CodeRabbit

* **Chores**
* Updated internal configuration import mechanism for sandbox provider
initialization. No end-user impact.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

agent/sandbox/providers/self_managed.py

@@ -70,7 +70,7 @@ class SelfManagedProvider(SandboxProvider):
             # Try to fall back to SANDBOX_HOST from settings if we are using localhost
             if "localhost" in self.endpoint or "127.0.0.1" in self.endpoint:
                 try:
-                    from api import settings
+                    from common import settings
                     if settings.SANDBOX_HOST and settings.SANDBOX_HOST not in self.endpoint:
                         original_endpoint = self.endpoint
                         self.endpoint = f"http://{settings.SANDBOX_HOST}:9385"