Update citation format to Hugging Face standard

- Change from @techreport to @misc format
- Add DOI: 10.57967/hf/6599
- Update URL to Hugging Face Hub
- Include revision hash (0712d08)
- Set publisher as Hugging Face
- Apply consistently to both README.md and System Card

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

README.md

@@ -325,14 +325,12 @@ for text in examples:
 If you use this model, please cite:
 
 ```bibtex
-@techreport{underthesea2025sonarcore1,
-  title = {Sonar Core 1: A Vietnamese Text Classification Model using Machine Learning},
-  author = {Vu Anh},
-  year = {2025},
-  month = {September},
-  institution = {Underthesea},
-  version = {1.0},
-  url = {https://github.com/undertheseanlp/underthesea/},
-  keywords = {text classification, vietnamese nlp, machine learning, tf-idf, logistic regression}
+@misc{undertheseanlp_2025,
+    author       = { undertheseanlp },
+    title        = { sonar_core_1 (Revision 0712d08) },
+    year         = 2025,
+    url          = { https://huggingface.co/undertheseanlp/sonar_core_1 },
+    doi          = { 10.57967/hf/6599 },
+    publisher    = { Hugging Face }
 }
 ```

Sonar Core 1 - System Card.md

@@ -269,14 +269,12 @@ Model trained on publicly available VNTC and UTS2017_Bank datasets. Please refer
 If you use this model, please cite:
 
 ```bibtex
-@techreport{underthesea2025sonarcore1,
-  title = {Sonar Core 1: A Vietnamese Text Classification Model using Machine Learning},
-  author = {Vu Anh},
-  year = {2025},
-  month = {September},
-  institution = {Underthesea},
-  version = {1.0},
-  url = {https://github.com/undertheseanlp/underthesea/},
-  keywords = {text classification, vietnamese nlp, machine learning, tf-idf, logistic regression}
+@misc{undertheseanlp_2025,
+    author       = { undertheseanlp },
+    title        = { sonar_core_1 (Revision 0712d08) },
+    year         = 2025,
+    url          = { https://huggingface.co/undertheseanlp/sonar_core_1 },
+    doi          = { 10.57967/hf/6599 },
+    publisher    = { Hugging Face }
 }
 ```