Restore rac_rag.h accidentally deleted in PR #471 merge

The VAD PR branch was based on a commit predating #447 (RAG+CPP_optis)
and so did not have rac_rag.h. The merge preserved the deletion but
rac_rag_register.cpp still includes this header, breaking the build.
Restoring the file verbatim from main.

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

Author: sanchitmonga22

sdk/runanywhere-commons/include/rac/features/rag/rac_rag.h

@@ -0,0 +1,39 @@
+/**
+ * @file rac_rag.h
+ * @brief RunAnywhere Commons - RAG Pipeline Public API
+ *
+ * Registration and control functions for the RAG pipeline module.
+ */
+
+#ifndef RAC_RAG_H
+#define RAC_RAG_H
+
+#include "rac/core/rac_types.h"
+#include "rac/features/rag/rac_rag_pipeline.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief Register the RAG pipeline module
+ *
+ * Must be called before using RAG functionality.
+ * Also registers the ONNX embeddings service provider if available.
+ *
+ * @return RAC_SUCCESS on success, error code otherwise
+ */
+RAC_API rac_result_t rac_backend_rag_register(void);
+
+/**
+ * @brief Unregister the RAG pipeline module
+ *
+ * @return RAC_SUCCESS on success, error code otherwise
+ */
+RAC_API rac_result_t rac_backend_rag_unregister(void);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif // RAC_RAG_H