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