fix(paths): keep business paths forward-slashed on Windows

Four places produced the host's separator (or a mixed path) where the app's
business form is forward-slashed, so on Windows the value could not be compared
with the one the rest of the app stores:

* `ModelScanner._calculate_folder` matched `file_path.startswith(root)` as raw
  strings, so every forward-slashed path resolved to the library root and a
  moved model was filed under the root instead of its folder. It now compares
  root identities and slices the relative part off.
* `normalize_relative_folder` ran `os.path.normpath`, and ntpath folds forward
  slashes back to backslashes: every folder parameter (scoped scan, create,
  rename, delete) came back host-spelled and mismatched the stored folders.
* `_format_model_name_for_comfyui` returned `os.path.relpath` unchanged, so the
  checkpoint/unet nodes and the metadata node emitted `unet\base.safetensors`
  on Windows -- a name no ComfyUI widget list matches.
* `resolve_centralized_dir_for_dir` passed a component that spans two
  directories ("<library>/<component>") whole to `os.path.join`, leaving a mixed
  path ("...\comfyui/loras-1a2b3c4d\sub") that no native path equals.

Also hands the rename re-key callback business paths, like every other absolute
path the move service returns.

py/utils/utils.py

@@ -303,8 +303,10 @@ def _format_model_name_for_comfyui(file_path: str, model_roots: list[str]) -> st
                 norm_root += os.sep
 
             if norm_file.startswith(norm_root):
-                # Use os.path.relpath to get relative path with OS-native separator
-                return os.path.relpath(file_path, root)
+                # ComfyUI names a model with forward slashes on every platform
+                # ("unet/base.safetensors"); os.path.relpath alone returns the
+                # host's separator, which no ComfyUI widget list matches on Windows.
+                return os.path.relpath(file_path, root).replace(os.sep, "/")
         except (ValueError, TypeError):
             continue