* Studio: decide diffusion routing before the SWA resolver
Loading a DiffusionGemma GGUF could fail with "llama-server failed to start. Check that the GGUF file is valid" while llama-diffusion-cli ran the same model fine.
_read_gguf_metadata set self._is_diffusion after calling _resolve_swa_pattern, both inside one try/except. The resolver reaches into transformers/HF, which can raise for an architecture transformers does not know (diffusion-gemma); the shared except then swallowed it and left _is_diffusion False, so the model was routed to plain llama-server instead of the diffusion runner. It only reproduced where the SWA pattern was not already cached/inline.
Set _is_diffusion right after the KV parse loop (before the resolver) so a resolver error can no longer drop the routing, and skip the resolver for diffusion models, which do not use Studio's SWA pattern.
* [pre-commit.ci] auto fixes from pre-commit.com hooks
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