docs: add code DOI badge and CITATION.cff

Adds the Zenodo code-release DOI 10.5281/zenodo.20019817 (minted
automatically by the GitHub-Zenodo integration when v0.4.1 was
published) as a second badge alongside the existing dataset DOI.

CITATION.cff lists both DOIs (code + dataset) so GitHub renders a
'Cite this repository' button with APA and BibTeX exports.

Author: SigmaJahan

CITATION.cff

@@ -0,0 +1,27 @@
+cff-version: 1.2.0
+message: "If you use this software, please cite both the code and the dataset."
+title: "DEFault++: Hierarchical fault diagnosis and runtime feature extraction for HuggingFace transformers"
+authors:
+  - family-names: Jahan
+    given-names: Sigma
+type: software
+version: "0.4.1"
+date-released: "2026-05-04"
+license: Apache-2.0
+repository-code: "https://github.com/SigmaJahan/DEFaultplusplus-Transformer-Debugging"
+identifiers:
+  - type: doi
+    value: 10.5281/zenodo.20019817
+    description: Code release v0.4.1 archived on Zenodo.
+  - type: doi
+    value: 10.5281/zenodo.20018623
+    description: DEFault++ benchmark v1 dataset on Zenodo (paper-aligned feature CSVs).
+keywords:
+  - transformer
+  - fault diagnosis
+  - fault detection
+  - deep learning debugging
+  - huggingface
+  - fine-tuning
+  - feature extraction
+  - training monitoring

defaultplusplus/README.md

@@ -1,6 +1,7 @@
 # defaultplusplus
 
 [![CI](https://github.com/SigmaJahan/DEFaultplusplus-Transformer-Debugging/actions/workflows/ci.yml/badge.svg?branch=main)](https://github.com/SigmaJahan/DEFaultplusplus-Transformer-Debugging/actions/workflows/ci.yml)
+[![Code DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.20019817.svg)](https://doi.org/10.5281/zenodo.20019817)
 [![Dataset DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.20018623.svg)](https://doi.org/10.5281/zenodo.20018623)
 
 Hierarchical fault diagnosis and runtime feature extraction for