✨ Add structural organization headers to 13_kernels module

- Added ## 🔧 DEVELOPMENT section before Step 1 where development begins
- Added ## 🤖 AUTO TESTING section before nbgrader block
- Updated to ## 🎯 MODULE SUMMARY: Hardware-Optimized Operations

Improves notebook organization without changing any code logic or content.

modules/source/13_kernels/kernels_dev.py

@@ -175,6 +175,11 @@ GPU kernels:         1000x speed (massive parallelism)
 Let's build the optimizations that power modern AI!
 """
 
+# %% [markdown]
+"""
+## 🔧 DEVELOPMENT
+"""
+
 # %% [markdown]
 """
 ## Step 1: Custom Operations - Beyond NumPy
@@ -1387,6 +1392,11 @@ Time to test your implementation! This section uses TinyTorch's standardized tes
 **This testing section is locked** - it provides consistent feedback across all modules and cannot be modified.
 """
 
+# %% [markdown]
+"""
+## 🤖 AUTO TESTING
+"""
+
 # %% nbgrader={"grade": false, "grade_id": "standardized-testing", "locked": true, "schema_version": 3, "solution": false, "task": false}
 # =============================================================================
 # STANDARDIZED MODULE TESTING - DO NOT MODIFY
@@ -1411,7 +1421,7 @@ if __name__ == "__main__":
 
 # %% [markdown]
 """
-## 🎯 Module Summary: Hardware-Optimized ML Operations
+## 🎯 MODULE SUMMARY: Hardware-Optimized Operations
 
 ### What You've Built
 You've implemented a complete set of hardware-optimized ML kernels: