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

install.sh

@@ -403,6 +403,15 @@ echo ""
 echo "release" > "$INSTALL_DIR/.release-channel"
 echo "$VERSION" > "$INSTALL_DIR/.release-version"
 
+# ── Hint about optional deps ──────────────────────────────────────────────────
+if [ -f "${INSTALL_DIR}/requirements-optional.txt" ]; then
+    echo ""
+    info "💡 Optional GPU/ML dependencies available:"
+    info "   ${INSTALL_DIR}/requirements-optional.txt"
+    echo "   Install them manually if you use the Orpheus TTS plugin:"
+    echo "     cd ${INSTALL_DIR} && .venv/bin/pip install -r requirements-optional.txt"
+fi
+
 echo "  Server : ${INSTALL_DIR}/run.sh"
 echo "  Binary : ${INSTALL_DIR}/bin/skald"
 echo "  Setup  : ${INSTALL_DIR}/bin/skald-setup"