## Summary
`<input type=\"file\">` inside front-components was silently
non-functional:
- The host-side `serializeEvent` did not read `target.files`, so the
worker received an empty `onChange` detail.
- `SerializedEventData` had no `files` field.
- The `html-input` schema in `AllowedHtmlElements` exposed neither
`accept`, `multiple`, nor `capture` — the worker could not even
configure the picker.
This PR forwards file metadata (`name`, `size`, `type`, `lastModified`)
through the existing serialized event detail and accepts the missing
attributes on the `html-input` remote element. A new Storybook play test
guards the regression by uploading single and multiple files via
`userEvent.upload`.
Reading file contents inside the worker is intentionally out of scope
here and will need a separate host API bridge (the host has the `File`
objects on the real input element; passing bytes through `postMessage`
is a bigger design call).
