Top-level imports; catch only expected exceptions

velopack/tracerite/fastapi-vue are always available in the GUI build, so
drop the in-function import guards. The update checker now catches only
RuntimeError (not a Velopack install: dev/portable) and OSError
(network). Build script and PyInstaller spec use platformdirs for the
persistent tool cache.

scripts/MediaHive.spec

@@ -7,7 +7,6 @@
 # Or use the build script (recommended—handles versioning and packaging):
 #   uv run scripts/guibuild.py
 
-import os
 import sys
 import mediahive.winmain
 import mediahive.server
@@ -23,11 +22,9 @@ _icon_win = _pkg / "assets" / "mediahive.ico"
 _icon_mac = _pkg / "assets" / "mediahive.icns"
 # ffmpeg staging lives in the persistent build cache (same logic as
 # scripts/guibuild.py); fall back to the legacy build/ffmpeg location.
-if sys.platform == "win32":
-    _cache_base = Path(os.environ.get("LOCALAPPDATA", Path.home() / "AppData" / "Local"))
-else:
-    _cache_base = Path(os.environ.get("XDG_CACHE_HOME", Path.home() / ".cache"))
-_tools_dir = _cache_base / "mediahive-build" / "ffmpeg"
+from platformdirs import user_cache_path
+
+_tools_dir = user_cache_path("mediahive-build") / "ffmpeg"
 if not _tools_dir.exists():
     _tools_dir = Path(SPECPATH).parent / "build" / "ffmpeg"
 _tool_names = ["ffmpeg.exe"] if sys.platform == "win32" else ["ffmpeg"]