expose NQL grammar

server/api/routes/search.py

 import httpx
+from nacsos_data.db.crud.items.query.parse import GRAMMAR
 from pydantic import BaseModel
 from fastapi import APIRouter, Depends
 import sqlalchemy.sql.functions as func
@@ -79,6 +80,11 @@ async def term_expansion(term_prefix: str,
         ]
 
 
+@router.get('/nql/grammar', response_model=str)
+async def nql_grammar() -> str:
+    return GRAMMAR
+
+
 class QueryResult(BaseModel):
     n_docs: int
     docs: list[AcademicItemModel]