set_image_model keys config by path:

    self.config[f"image:{model_name}"] = config or {}

so a second image_models entry for the same checkpoint overwrote the first and
said nothing. Two configs of one checkpoint is not an odd thing to want -- the
same base served with a different transformer, quantization or step count --
and text models have supported it for a long time, addressing the second under
its alias and skipping an unaliased duplicate with a message. Image models had
none of that.

The symptom is worse than losing an entry, because nothing looks lost: both
entries still appear in /v1/models and both register their aliases, so a
request for EITHER is answered with whichever config was registered last.
Found while testing two configs of Qwen-Image-Edit-2511, one with a GGUF
transformer and one with a fine-tuned transformer quantized at load: a request
for the GGUF config was served by the 4-bit one, and the only clue was
"Registered image model: Qwen/Qwen-Image-Edit-2511" appearing twice in the
startup log.

So the image path now does what the text path does: a sibling sharing a
checkpoint is registered under its alias, which gives it a config key of its
own, and is NOT aliased back to the shared path -- that mapping is what
collapses the two again. An unaliased duplicate is skipped with the same
explanation text models give.

`path` now travels in every image config, because a sibling is addressed by an
alias and an alias is not something from_pretrained can open: the config has to
be able to say which checkpoint it is a config OF. _load_diffusers_pipeline
prefers it when it differs from the name it was called with, and for a primary
entry the two are the same string.

Needs a restart to take effect, registration being a startup act: a collision
that has already happened cannot be undone in the running process's config
dict.

Full suite 4558 passed with the same 15 pre-existing failures as 0.4.91 (diff
empty).
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S8LAP3ueNzQJtwzhgVbq66