chore: ignore generated ORT engine cache

ort_cache/ holds .ort engines built on first run from the .onnx models.
They are machine- and version-specific build products, not sources.

.gitignore

@@ -27,3 +27,4 @@ Thumbs.db
 
 # Claude Code local settings
 .claude/settings.local.json
+include/kpn/ort_cache/