Rename storage_exp/ to store/, remove unused storage/

Update all active scripts, .gitignore, CLAUDE.md, and README.md.
Also fix stale filename references in script header comments.

retrieve.py

@@ -1,9 +1,9 @@
-# retrieve_hybrid_raw.py
+# retrieve.py
 # Hybrid verbatim chunk retrieval: BM25 + vector search + cross-encoder, no LLM.
 #
-# Same hybrid retrieval as query_hybrid_bm25_v4.py but outputs raw chunk text
+# Same hybrid retrieval as query_hybrid.py but outputs raw chunk text
 # instead of LLM synthesis. Useful for inspecting what the hybrid pipeline
-# retrieves and comparing against retrieve_raw.py (vector-only).
+# retrieves.
 #
 # Each chunk is annotated with its source (vector, BM25, or both) so you can
 # see which retriever nominated it.
@@ -33,7 +33,7 @@ import textwrap
 # Globals
 #
 
-# Embedding model (must match build_exp_claude.py)
+# Embedding model (must match build_store.py)
 EMBED_MODEL = HuggingFaceEmbedding(cache_folder="./models", model_name="BAAI/bge-large-en-v1.5", local_files_only=True)
 
 # Cross-encoder model for re-ranking (cached in ./models/)
@@ -53,7 +53,7 @@ def main():
     Settings.embed_model = EMBED_MODEL
 
     # Load persisted vector store
-    storage_context = StorageContext.from_defaults(persist_dir="./storage_exp")
+    storage_context = StorageContext.from_defaults(persist_dir="./store")
     index = load_index_from_storage(storage_context)
 
     # --- Retrievers ---