fix(lora): review findings for the LoraManager layout (#355)

- The example-images library subfolder goes through the folder guard like
  its root, so its canonical (normcased) form matches the media check on
  Windows for a library name with capitals.
- A failed trigger-word load is retried by a running node only after
  TRIGGER_RETRY_SECONDS, not on every prompt run.
- A review whose discovery cannot list a folder says so (folder-unreadable,
  the folder's name only) instead of a generic error.

py/api/lora_import_routes.py

@@ -230,6 +230,18 @@ class LoraImportRoutesMixin:
                 lora_import.preview, lm_path, cache_dir, SERVABLE_EXTENSIONS
             )
             state = await self._run_in_executor(db.category_import_state, CATEGORY)
+        except OSError as error:
+            # A folder discovery cannot list refuses the import (it must not
+            # replace the collection with part of it): say which one.
+            self.logger.warning(
+                f"LoRA import review: a folder could not be listed: {error}"
+            )
+            return _failure(
+                f"A LoRA folder could not be listed ({self._public_error(error)}). "
+                "Nothing was changed.",
+                500,
+                "folder-unreadable",
+            )
         except Exception:
             self.logger.exception("LoRA import preview failed")
             return _failure("The LoRA import could not be reviewed.", 500)