Asset browser can edit display name but cannot rename the underlying file

## Summary
In the current assets workflow, users can edit an asset's display name/metadata from the asset browser, but there is no supported way to rename the underlying file on disk.

This creates a gap between:
- what the asset browser shows as the editable/display-facing name, and
- what model loaders and workflow/runtime logic still use as the real filename

## Current behavior
Today, users can update asset metadata such as display name, but that does not rename the physical file in `ComfyUI/models/...`.

As a result:
- the asset browser can show a nicer or corrected name
- but the actual file basename on disk stays unchanged
- loaders that enumerate filenames from model folders still use the old basename
- workflows/custom nodes that depend on real filenames do not benefit from the display-name edit

## Why this matters
This is especially confusing in combination with:
- digest/content-addressed stored filenames
- custom nodes that expect exact filenames
- assets where `display_name` / metadata name differs from the real filename

Users can reasonably assume that editing a model's name in the UI should also let them fix the actual model filename, but currently that is not possible.

## Expected behavior
ComfyUI should provide a supported way to rename the underlying asset file, at least for model assets.

That operation should:
- rename the physical file on disk
- update the active asset reference `file_path`
- update filename metadata to match
- handle collisions safely
- keep asset browser metadata and runtime-visible filenames consistent

## Scope suggestion
This could be implemented as either:
- a dedicated backend endpoint for file rename, or
- a supported assets API operation distinct from display-name metadata editing

The important distinction is that:
- editing display name / metadata is not the same thing as
- renaming the real file basename used by model loaders

## Related issues
- digest filenames vs original filenames: #13183
- model type change does not move file to the new folder: #13185