Keep scan terminal lint clean after helper split

The AI helper extraction left a stale private helper import in the scan terminal service. Removing it keeps CI aligned with the current call graph without changing runtime behavior.

Constraint: CI runs ruff F401 as a blocking check.
Confidence: high
Scope-risk: narrow
Reversibility: clean
Tested: .\.codex-tmp\pydeps\bin\ruff.exe check .
Not-tested: Full backend test suite; change is import-only.

web/scan_terminal_service.py

@@ -29,7 +29,6 @@ from web.scan_city_ai_helpers import (
     _extract_provider_stream_delta,
     _provider_response_meta,
     _safe_float,
-    _strip_incomplete_ai_sentence,
     _truncate_ai_text,
 )