fix(copilot): fix stream_err UnboundLocalError, move local import to top-level

Python 3 deletes `except ... as e` bindings after the except block
exits (PEP 3110). Save the exception to a persistent variable so
the for...else exhaustion block can reference it.

Also move `from backend.copilot.config import ChatConfig` from a
local import to top-level in transcript.py.

autogpt_platform/backend/backend/copilot/sdk/service.py

@@ -1409,7 +1409,8 @@ async def stream_chat_completion_sdk(
                     _MAX_STREAM_ATTEMPTS,
                 )
                 raise
-            except Exception as stream_err:
+            except Exception as e:
+                stream_err = e
                 logger.warning(
                     "%s Stream error (attempt %d/%d): %s",
                     log_prefix,

autogpt_platform/backend/backend/copilot/sdk/transcript.py

@@ -21,6 +21,7 @@ from dataclasses import dataclass
 from pathlib import Path
 from uuid import uuid4
 
+from backend.copilot.config import ChatConfig
 from backend.util import json
 from backend.util.clients import get_openai_client
 from backend.util.prompt import CompressResult, compress_context
@@ -734,8 +735,6 @@ async def compact_transcript(
 
     Returns the compacted JSONL string, or ``None`` on failure.
     """
-    from backend.copilot.config import ChatConfig
-
     cfg = ChatConfig()
     messages = _transcript_to_messages(content)
     if len(messages) < 2: