feat: add RAG_RERANKING_BATCH_SIZE configuration option

Add configurable reranker batch size (env var RAG_RERANKING_BATCH_SIZE,
default 32) following the same pattern as RAG_EMBEDDING_BATCH_SIZE.

- config.py: PersistentConfig for RAG_RERANKING_BATCH_SIZE
- main.py: import, state init, pass to get_reranking_function
- colbert.py: accept batch_size param in predict() (was hardcoded 32)
- utils.py: get_reranking_function passes batch_size at call time
- retrieval.py: expose in config GET/POST endpoints and ConfigForm
- Documents.svelte: add Reranking Batch Size input in admin settings

Closes #23730

backend/open_webui/main.py

@@ -248,6 +248,7 @@ from open_webui.config import (
     RAG_EXTERNAL_RERANKER_URL,
     RAG_EXTERNAL_RERANKER_API_KEY,
     RAG_EXTERNAL_RERANKER_TIMEOUT,
+    RAG_RERANKING_BATCH_SIZE,
     RAG_RERANKING_MODEL_AUTO_UPDATE,
     RAG_RERANKING_MODEL_TRUST_REMOTE_CODE,
     RAG_EMBEDDING_ENGINE,
@@ -1044,6 +1045,7 @@ app.state.config.RAG_RERANKING_MODEL = RAG_RERANKING_MODEL
 app.state.config.RAG_EXTERNAL_RERANKER_URL = RAG_EXTERNAL_RERANKER_URL
 app.state.config.RAG_EXTERNAL_RERANKER_API_KEY = RAG_EXTERNAL_RERANKER_API_KEY
 app.state.config.RAG_EXTERNAL_RERANKER_TIMEOUT = RAG_EXTERNAL_RERANKER_TIMEOUT
+app.state.config.RAG_RERANKING_BATCH_SIZE = RAG_RERANKING_BATCH_SIZE
 
 app.state.config.RAG_TEMPLATE = RAG_TEMPLATE
 
@@ -1193,6 +1195,7 @@ app.state.RERANKING_FUNCTION = get_reranking_function(
     app.state.config.RAG_RERANKING_ENGINE,
     app.state.config.RAG_RERANKING_MODEL,
     reranking_function=app.state.rf,
+    reranking_batch_size=app.state.config.RAG_RERANKING_BATCH_SIZE,
 )
 
 ########################################