Add setup-venv.sh, clean up setup-venv-local-build.sh

setup-venv.sh: simple PyPI install path — just pip install faster-whisper.
Use this when the PyPI ctranslate2 wheel matches the system CUDA version.

setup-venv-local-build.sh:
- PYTHON_ENV env var for venv path override (consistent with tts-server)
- HF_TOKEN_FILE env var instead of hardcoded path
- HF_HUB_CACHE env var surfaced in output when set
- Remove stray chmod on faster-whisper-server.py (not part of this repo)
- Remove voice-experiment-specific "run with" message
- Add python3 to tool prerequisite check
- Arch Linux package suggestions extended to cover CUDA and python
- Document why each script exists and when to use which

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

setup-venv.sh

@@ -0,0 +1,34 @@
+#!/usr/bin/env bash
+#
+# setup-venv.sh — installs faster-whisper from PyPI into a venv.
+#
+# USE THIS SCRIPT when the PyPI ctranslate2 wheel matches your CUDA version.
+# PyPI wheels target a specific CUDA major version; if your system matches,
+# this is the fastest way to get started — no compilation required.
+#
+# If you see errors like "libcublas.so.12: cannot open shared object file" at
+# runtime, your CUDA version does not match the wheel. Use setup-venv-local-build.sh
+# instead, which compiles ctranslate2 against your actual CUDA installation.
+#
+# Environment overrides:
+#   PYTHON_ENV      path to venv (default: ./venv)
+#
+# Arch Linux packages needed before running this script:
+#   sudo pacman -S python cuda
+#
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+VENV="${PYTHON_ENV:-${SCRIPT_DIR}/venv}"
+
+if [ ! -d "${VENV}" ]; then
+	echo "==> creating venv at ${VENV}"
+	python3 -m venv "${VENV}"
+fi
+
+echo "==> installing faster-whisper"
+"${VENV}/bin/pip" install --upgrade pip --quiet
+"${VENV}/bin/pip" install faster-whisper
+
+echo ""
+echo "==> done. Venv ready at ${VENV}"