refactor: Remove stopwords_interaction_guide.md references and fix comment

Two improvements:

1. Remove all references to docs/stopwords_interaction_guide.md
   - Removed from docs/api/query.rst (HybridQuery and TextQuery notes)
   - Removed from docs/api/schema.rst (replaced with reference to user guide)
   - Removed from redisvl/query/query.py (TextQuery docstring)
   - Removed from redisvl/query/aggregate.py (AggregateHybridQuery docstring)
   - Removed from redisvl/index/index.py (warning message)
   - Removed from docs/user_guide/11_advanced_queries.ipynb
   - The notebook already has comprehensive stopwords documentation

2. Fix inaccurate comment about stopwords=None
   - Updated comment in redisvl/index/index.py to clarify that ANY falsy
     value (None, False, '', 0, [], etc.) results in an empty set, not just None
   - This matches the actual implementation in _set_stopwords() which uses
     'if not stopwords:' check
   - Updated warning message to mention 'stopwords=None (or any falsy value)'

Author: nkanu17

docs/api/query.rst

@@ -51,7 +51,6 @@ HybridQuery
    The ``stopwords`` parameter in :class:`HybridQuery` (and :class:`AggregateHybridQuery`) controls query-time stopword filtering (client-side).
    For index-level stopwords configuration (server-side), see :class:`redisvl.schema.IndexInfo.stopwords`.
    Using query-time stopwords with index-level ``STOPWORDS 0`` is counterproductive.
-   See the `Stopwords Interaction Guide <../stopwords_interaction_guide.html>`_ for details.
 
 
 TextQuery
@@ -71,7 +70,6 @@ TextQuery
    The ``stopwords`` parameter in :class:`TextQuery` controls query-time stopword filtering (client-side).
    For index-level stopwords configuration (server-side), see :class:`redisvl.schema.IndexInfo.stopwords`.
    Using query-time stopwords with index-level ``STOPWORDS 0`` is counterproductive.
-   See the `Stopwords Interaction Guide <../stopwords_interaction_guide.html>`_ for details.
 
 
 FilterQuery

docs/api/schema.rst

@@ -65,11 +65,11 @@ the ``stopwords`` field. This controls which words are filtered during indexing
 **Important Notes:**
 
 - Index-level stopwords affect what gets indexed (server-side)
-- Query-time stopwords (in :class:`TextQuery`) affect what gets searched (client-side)
+- Query-time stopwords (in :class:`TextQuery` and :class:`AggregateHybridQuery`) affect what gets searched (client-side)
 - Using query-time stopwords with index-level ``STOPWORDS 0`` is counterproductive
 
 For detailed information about stopwords configuration and best practices, see the
-`Stopwords Interaction Guide <../stopwords_interaction_guide.html>`_.
+Advanced Queries user guide (``docs/user_guide/11_advanced_queries.ipynb``).
 
 
 Defining Fields