[Bug] MacOS Failure due to bad linking.

### Git commit

Latest.

Root cause: the prebuilt sd-server binary in .cache/bin/sd-cpp/metal/ was linked on the CI runner with a hardcoded LC_RPATH of
  /Users/runner/work/stable-diffusion.cpp/.../build/bin and no @executable_path rpath, so it can't find the libstable-diffusion.dylib sitting right next to it.
  Lemonade's SDServer does try to compensate by exporting LD_LIBRARY_PATH — but that's the Linux env var; macOS's dyld uses DYLD_LIBRARY_PATH, so the workaround
  never fires (and would be stripped by SIP for system binaries anyway).

Ps. I fixed these on the lemonade ci pipeline process.

### Operating System & Version

MacOS 26.5

### GGML backends

Metal

### Command-line arguments used

/Library/Application Support/lemonade/.cache/bin/sd-cpp/metal/sd-server" --listen-port 8001 --diffusion-model "xxxxx"

### Steps to reproduce

run the binary on mac / metal.

### What you expected to happen

to work.

### What actually happened

it broke.

### Logs / error messages / stack trace

_No response_

### Additional context / environment details

_No response_

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