chore: configure bge-large as default embedding model

Sets Xenova/bge-large-en-v1.5 (1024d) as the default embedding model
for codegraph self-analysis, replacing the default minilm.

Author: github-actions[bot]

.codegraphrc.json

@@ -0,0 +1,3 @@
+{
+  "embeddings": { "model": "bge-large" }
+}