Qwen3.5 models deployed via vLLM natively support image input, but the
supportsImageInput() check was incorrectly blocking them. The function
only exempted qwen3.5-plus and qwen3.5-flash variants, missing the base
qwen3.5 model name.
Simplify the exception to cover all qwen3.5 variants with a single
substring check on "qwen3.5", since it is a common prefix of all three.
Co-authored-by: octo-patch <octo-patch@github.com>