ui: Correct links in tools/ui/README.md [no ci] (ggml-org#23139)

In `tools/ui/README.md`, update the relative links, now that the `README.md` file has been moved from `tools/server/webui/` to `tools/ui/`.

See ggml-org@59778f0.

Author: howlger

tools/ui/README.md

@@ -681,6 +681,6 @@ tools/ui/
 
 ## Related Documentation
 
-- [llama.cpp Server README](../README.md) - Full server documentation
-- [Multimodal Documentation](../../../docs/multimodal.md) - Image and audio support
-- [Function Calling](../../../docs/function-calling.md) - Tool use capabilities
+- [llama.cpp Server README](../server/README.md) - Full server documentation
+- [Multimodal Documentation](../../docs/multimodal.md) - Image and audio support
+- [Function Calling](../../docs/function-calling.md) - Tool use capabilities