fix: remove all remaining mistralrs-server references

Drop Obsoletes/Provides for the old package name and update readme
and UI to use mistralrs-cuda13 consistently.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

rpm/mistralrs.spec

@@ -29,8 +29,6 @@ ExclusiveArch:  x86_64
 %global __requires_exclude ^lib(cuda|cudart|cudnn|cublas|cublasLt|curand|nvrtc|nccl)
 Requires:       systemd
 
-Obsoletes:      mistralrs-server-%{mistralrs_flavour} < %{version}-%{release}
-Provides:       mistralrs-server-%{mistralrs_flavour} = %{version}-%{release}
 
 %description
 mistral.rs is a blazingly fast LLM inference engine written in Rust.