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.

py/lora_manager_layout.py

@@ -577,7 +577,7 @@ def _preview_candidates(sidecar: Sidecar, metadata: Dict) -> Iterator[str]:
             # LoraManager writes absolute paths; it would resolve a relative
             # one against its working directory, not the sidecar folder.
             logger.debug(
-                f"Relative preview_url skipped in {sidecar.metadata_path.name}"
+                "Relative preview_url skipped in %s", sidecar.metadata_path.name
             )
     base = sidecar.metadata_path.name[: -len(METADATA_SUFFIX)]
     for suffix in PREVIEW_EXTENSIONS:

py/lora_utils.py

@@ -368,7 +368,7 @@ def read_lora_metadata(metadata_path: Path) -> Optional[Dict]:
     try:
         with open(metadata_path, "r", encoding="utf-8") as f:
             return json.load(f)
-    except (json.JSONDecodeError, OSError) as e:
+    except (ValueError, OSError) as e:  # JSONDecodeError, UnicodeDecodeError
         logger.debug(f"Failed to read {metadata_path}: {e}")
         return None