[gallery] Fix duplicate sha256 keys in Wan models (#9461)

Fix duplicate sha256 keys in wan models gallery

The wan models previously defined the `sha256` key twice in their files lists,
which triggered strict mapping key checks in the YAML parser and resulted
in unmarshal errors that crashed the `/api/models` loading. This removes
the redundant trailing `sha256` keys from the Wan model definitions.

Assisted-by: Antigravity:Gemini-3.1-Pro-High [multi_replace_file_content, run_command]

Signed-off-by: Alex <codecrusher24@gmail.com>