fix: honor reference image resize opt-out in server requests

[AzizMuminov]

Summary

• Make auto_resize_ref_image: false preserve native dimensions for native ref_images and SDAPI extra_images.
• Preserve the existing default behavior when auto_resize_ref_image is enabled or omitted.
• Keep the OpenAI edits route unchanged because it also establishes generic init_image/img2img semantics.

Related Issue / Discussion

Related to #2004.

The server previously resized base64 reference images to the requested output size during decode. This occurred before the later resize_before_vae option was evaluated, so setting auto_resize_ref_image: false could not restore the original pixels. For PiD, which bypasses the later reference-VAE resize path, the prematurely upscaled reference was encoded directly.

This intentionally takes the compatibility-preserving approach: the existing opt-out now works, while default server requests retain their current behavior. It differs from #2007, which proposes preserving native reference dimensions by default.

Verification

• Parser-level probe using a 1x1 PNG and a 1536x1152 request:
  • default behavior: reference is resized to 1536x1152;
  • auto_resize_ref_image: false: reference remains 1x1 through the generation request.
• cmake --build build_issue2004 --target sd-server -j 4 with SD_METAL=ON.
• git diff --check.

Full PiD image-quality verification was not run because the required PiD model weights are not available locally.

[leejet]

Thank you for your contribution.