Allow to disable reranking by having an empty provider

docs/configuration.md

@@ -109,6 +109,14 @@ Reranking improves search quality by re-ordering the initial search results usin
 
 Reranking is **automatically enabled** by default using Ollama, or if you install the appropriate reranking provider package.
 
+### Disabling Reranking
+
+To disable reranking completely for faster searches:
+
+```bash
+RERANK_PROVIDER=""
+```
+
 ### Ollama (Default)
 
 Ollama reranking uses LLMs with structured output to rank documents by relevance:

src/haiku/rag/reranking/__init__.py

@@ -1,22 +1,18 @@
 from haiku.rag.config import Config
 from haiku.rag.reranking.base import RerankerBase
 
-try:
-    from haiku.rag.reranking.cohere import CohereReranker
-except ImportError:
-    pass
-
 _reranker: RerankerBase | None = None
 
 
 def get_reranker() -> RerankerBase | None:
     """
     Factory function to get the appropriate reranker based on the configuration.
-    Returns None if the required package is not available.
+    Returns None if if reranking is disabled.
     """
     global _reranker
     if _reranker is not None:
         return _reranker
+
     if Config.RERANK_PROVIDER == "mxbai":
         try:
             from haiku.rag.reranking.mxbai import MxBAIReranker