Add separate requirements for the scheduled refresh job

requirements_hf.txt pins versions for the Space's Python 3.9 container
(numpy 1.26.4, faiss-cpu 1.7.4). Those pins cannot build on the refresh box,
which runs Python 3.14, and the refresh job does not need flask, openai, or
faster-whisper anyway.

Only the FAISS index format crosses between the two, and it is stable across
these ranges: build with modern versions, serve with the pinned ones.

requirements_refresh.txt

@@ -0,0 +1,22 @@
+# Dependencies for the scheduled refresh job only (download + build_index).
+#
+# Deliberately separate from requirements_hf.txt, which pins old versions for
+# the Space's Python 3.9 container (numpy 1.26.4, faiss-cpu 1.7.4). Those pins
+# cannot build on a modern interpreter, and the refresh box runs Python 3.14.
+#
+# The refresh job never imports flask, openai, or faster-whisper; it only needs
+# to fetch sources and write a FAISS index. Nothing here affects the deployed
+# Space, which still installs requirements_hf.txt inside its own container.
+#
+# The index format is what crosses between them, and it is stable across these
+# version ranges: build here, serve there.
+
+requests>=2.31.0
+python-dotenv>=1.0.1
+beautifulsoup4>=4.12.2
+numpy>=1.26
+faiss-cpu>=1.7.4
+cohere>=4.57
+langchain-community>=0.3.14
+langchain-text-splitters>=0.3.0
+PyPDF2>=3.0.1