Update addon tests, bootstrap runtime, download progress, and worker functionality

- Modified status messages and stage labels in `test_addon.py` for clarity and consistency.
- Added tests to ensure proper host termination and command execution in `test_addon.py`.
- Enhanced `test_bootstrap_runtime.py` with additional tests for installation behavior, including handling of CUDA and MPS devices, and improved error handling for disk space and network checks.
- Updated download progress reporting in `test_download_progress.py` to include download speed and improved message formatting.
- Added new tests in `test_worker.py` for device selection, NPZ file validation, and model downloading behavior with Hugging Face endpoints.
- Bumped version in `uv.lock` to 0.9.30.

src/snapform/preferences.py

@@ -1,4 +1,5 @@
 import shutil
+import sys
 from pathlib import Path
 
 import bpy
@@ -18,9 +19,12 @@ class SnapFormPreferences(bpy.types.AddonPreferences):
     )
     uv_executable: bpy.props.StringProperty(
         name="uv Executable",
-        description="Path to uv; a command name is accepted when uv is on PATH",
+        description=(
+            "Path to uv; leave empty to auto-download a standalone uv "
+            "when it is missing"
+        ),
         subtype="FILE_PATH",
-        default=shutil.which("uv") or "uv",
+        default=shutil.which("uv") or "",
     )
     torch_backend: bpy.props.EnumProperty(
         name="Torch Backend",
@@ -29,7 +33,7 @@ class SnapFormPreferences(bpy.types.AddonPreferences):
             ("CU128", "CUDA 12.8", "NVIDIA CUDA 12.8 PyTorch wheels"),
             ("CPU", "CPU", "CPU-only PyTorch wheels"),
         ),
-        default="CU128",
+        default="CPU" if sys.platform == "darwin" else "CU128",
     )
 
     def draw(self, _context):