fix(scripts): calibrate_ask.py SQL ::timestamptz cast 파싱 충돌 해소

SQLAlchemy text() 의 `:name` 파라미터가 PostgreSQL `::type` cast 와
토큰 경계 충돌로 치환되지 않아 `syntax error at or near ":"` 발생.
`:since::timestamptz` → `CAST(:since AS TIMESTAMPTZ)` 로 변경.

Reproduction: --since/--until 옵션 사용 시 모든 집계 쿼리 실패.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/calibrate_ask.py

@@ -109,8 +109,8 @@ def build_filters(args: argparse.Namespace) -> tuple[str, dict[str, Any]]:
     clauses = [
         "(:source IS NULL OR source = :source)",
         "(:prompt_version IS NULL OR prompt_version = :prompt_version)",
-        "(:since IS NULL OR created_at >= :since::timestamptz)",
-        "(:until IS NULL OR created_at < :until::timestamptz)",
+        "(:since IS NULL OR created_at >= CAST(:since AS TIMESTAMPTZ))",
+        "(:until IS NULL OR created_at < CAST(:until AS TIMESTAMPTZ))",
     ]
     params: dict[str, Any] = {
         "source": args.source,