Move build_pipeline.py into Pipeline directory

Readme.MD

@@ -58,7 +58,8 @@ payguard-fraud-detection/
 │
 ├── app.py                  # FastAPI application
 ├── preprocessing.py        # Model training & threshold optimization
-├── build_pipeline.py       # Sklearn pipeline definition
+├──Pipeline/
+    ├── build_pipeline.py       # Sklearn pipeline definition
 ├── requirements.txt        # Python dependencies
 │
 ├── index.html              # User-facing frontend
@@ -270,4 +271,4 @@ This project is licensed under the MIT License.
 
 ---
 
-> ⚡ Built as a portfolio project demonstrating end-to-end ML system design, REST API development, and payment gateway-inspired UI — not affiliated with Razorpay Pvt. Ltd.
+> ⚡ Built as a portfolio project demonstrating end-to-end ML system design, REST API development, and payment gateway-inspired UI — not affiliated with Razorpay Pvt. Ltd.