Fix build script: remove duplicate 'install' arg, fix Windows shell

- build_sidecar.py: pip_install() now includes 'install' in the command,
  callers pass only package names (was doubling up as 'uv pip install install torch')
- CI: set shell: bash on uv steps so Windows doesn't try to use cmd.exe

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

python/build_sidecar.py

@@ -96,30 +96,31 @@ def create_venv_and_install(cpu_only: bool) -> Path:
     else:
         python = str(venv_dir / "bin" / "python")
 
-    def pkg_install(*args: str) -> None:
+    def pip_install(*args: str) -> None:
+        """Install packages. Pass package names and flags only, not 'install'."""
         if use_uv:
             subprocess.run(["uv", "pip", "install", "--python", python, *args], check=True)
         else:
-            subprocess.run([python, "-m", "pip", *args], check=True)
+            subprocess.run([python, "-m", "pip", "install", *args], check=True)
 
     if not use_uv:
         # Upgrade pip (uv doesn't need this)
-        pkg_install("install", "--upgrade", "pip", "setuptools", "wheel")
+        pip_install("--upgrade", "pip", "setuptools", "wheel")
 
     # Install torch (CPU-only to avoid bundling ~2GB of CUDA libs)
     if cpu_only:
         print("[build] Installing PyTorch (CPU-only)")
-        pkg_install(
-            "install", "torch", "torchaudio",
+        pip_install(
+            "torch", "torchaudio",
             "--index-url", "https://download.pytorch.org/whl/cpu",
         )
     else:
         print("[build] Installing PyTorch (default, may include CUDA)")
-        pkg_install("install", "torch", "torchaudio")
+        pip_install("torch", "torchaudio")
 
     # Install project and dev deps (includes pyinstaller)
     print("[build] Installing project dependencies")
-    pkg_install("install", "-e", f"{SCRIPT_DIR}[dev]")
+    pip_install("-e", f"{SCRIPT_DIR}[dev]")
 
     return Path(python)