Pin accelerate and peft to release versions instead of git HEAD

Both were installed via unpinned git+https://..., so every fresh build
silently pulled whatever was on GitHub main that day — the same class
of drift that caused today's diffusers/huggingface-hub conflict. This
Space went 5 weeks without a rebuild before today's AWS-outage-forced
restart pulled a month of accumulated upstream changes at once; pinning
accelerate/peft closes off that same failure mode for accelerate/peft
specifically.

Pinned to the latest released versions (accelerate==1.14.0, which the
unpinned build had already drifted past to 1.15.0.dev0; peft==0.19.1,
past 0.19.2.dev0). Verified via a real pip dry-run resolve alongside
diffusers==0.39.0 and transformers==4.57.1 that this combination
resolves cleanly with no conflicts. Neither package is imported
directly anywhere in this repo (they're consumed internally by
diffusers' ModelMixin/PeftAdapterMixin/QwenImageLoraLoaderMixin), and
diffusers 0.39.0 only requires accelerate>=0.31.0 and peft>=0.17.0, so
both releases are comfortably within range.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

requirements.txt

@@ -1,6 +1,6 @@
-git+https://github.com/huggingface/accelerate.git
+accelerate==1.14.0
 diffusers==0.39.0
-git+https://github.com/huggingface/peft.git
+peft==0.19.1
 transformers==4.57.1
 huggingface_hub
 pyarrow