Add section organization to 13_kernels module: Add DEVELOPMENT section header

- Insert ## 🔧 DEVELOPMENT header before first test function
- Organizes module according to educational structure guidelines
- Maintains all existing functionality and test execution
- Improves readability and navigation for educational use

modules/source/13_kernels/kernels_dev.py

@@ -278,6 +278,11 @@ def matmul_baseline(A: Tensor, B: Tensor) -> Tensor:
     return result
     ### END SOLUTION
 
+# %% [markdown]
+"""
+## 🔧 DEVELOPMENT
+"""
+
 # %% nbgrader={"grade": false, "grade_id": "test-custom-matmul", "locked": false, "schema_version": 3, "solution": false, "task": false}
 ### 🧪 Unit Test: Baseline Matrix Multiplication