feat: refine assistant logic and update docs

app/core/cleaner.py

@@ -342,6 +342,7 @@ def numbers_to_words(text: str) -> str:
         case = "nominative"
         gender = "m"
         prep_clean = prep.strip().lower() if prep else None
+        parsed = None
 
         if prep_clean:
             morph_case = get_case_from_preposition(prep_clean)
@@ -359,6 +360,7 @@ def numbers_to_words(text: str) -> str:
         # Спец-случай: "на 1 час"
         if (
             prep_clean == "на"
+            and parsed is not None
             and parsed.normal_form in TIME_UNIT_LEMMAS
             and parsed.tag.gender in ("masc", "neut")
         ):