Move heavy GPU deps (torch, bitsandbytes) to requirements-optional.txt

torch and bitsandbytes pull in hundreds of MB of CUDA libraries
(nvidia_cublas ~423 MB) which are useless on headless servers
without an NVIDIA GPU like the NiPoGi.

- requirements.txt: keep only lightweight essential dependencies
- requirements-optional.txt (new): Orpheus TTS deps (torch, transformers,
  bitsandbytes, snac, huggingface_hub)
- Installers and update.sh: show hint about optional deps after install
- ci/package.sh: include requirements-optional.txt in tarball

requirements.txt

@@ -16,12 +16,8 @@ trendspyg>=0.7.0
 kokoro-onnx
 soundfile
 
-# Orpheus TTS 3B (plugin-tts-orpheus-3b) — heavy deps, only needed when plugin is enabled
-torch
-transformers
-snac
-bitsandbytes
-huggingface_hub
+# Orpheus TTS 3B (plugin-tts-orpheus-3b) — heavy deps moved to requirements-optional.txt
+# See requirements-optional.txt if you need the Orpheus TTS plugin.
 fastapi
 uvicorn
 scipy