fix(lora): skip a sidecar that is not UTF-8 instead of failing the load (#362)

Review follow-up on phase 4: read_lora_metadata caught JSONDecodeError but not
UnicodeDecodeError, so one non-UTF-8 sidecar failed the whole trigger-word
load (now logged with a traceback every retry) and the import review. It is
skipped like any unreadable sidecar. The relative preview_url DEBUG line uses
lazy formatting.

tests/test_lora_layout_cache.py

@@ -15,8 +15,8 @@ import tempfile
 import threading
 import time
 import unittest
-from pathlib import Path, PureWindowsPath
 from dataclasses import replace
+from pathlib import Path, PureWindowsPath
 from types import SimpleNamespace
 from unittest.mock import patch