text: fix NameError — move 'import re as _re' to module top

The loop-guard change added a module-level _GEMMA_CALL_RE = _re.compile(...) at
the top of the file, but 'import re as _re' sat far below (line 2266), so import
crashed with NameError: name '_re' is not defined and every engine failed to
start. Move the import up with the other stdlib imports (removing the late
duplicate). Verified codai.api.text now imports cleanly.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RdMufYvtTbtGDWsiZVoXce

codai/api/text.py

@@ -21,6 +21,7 @@ Text generation endpoints for the codai API.
 import asyncio
 import json
 import logging
+import re as _re
 import time
 import uuid
 from typing import AsyncGenerator, Dict, List, Optional
@@ -2263,7 +2264,6 @@ async def chat_completions(request: ChatCompletionRequest, http_request: Request
         finally:
             _release_instance()
 
-import re as _re
 
 _TOOL_SPAN_RE = _re.compile(r'<(tool|tool_call)\b[\s\S]*?</\1\s*>', _re.IGNORECASE)
 _TOOL_OPEN_RE = _re.compile(r'<(?:tool|tool_call)\b', _re.IGNORECASE)