Add consistent 'Ready to Build?' endings to README modules

Standardize module endings with motivational section + grid cards:

Added to 4 key modules:
- 01_setup: Foundation workflow mastery message
- 03_activations: Neural networks come alive message
- 06_cnn: Computer vision implementation message
- 09_optimizers: Learning algorithms message

Standard Format:
## 🎉 Ready to Build?
[Module-specific motivational content about what they're building]
Take your time, test thoroughly, and enjoy building something that really works! 🔥

[Grid cards automatically follow via converter]

Progress: 6/14 modules now have consistent endings
- ✅ 01_setup, 02_tensor, 03_activations, 06_cnn, 07_dataloader, 09_optimizers
- 🔄 8 more modules to standardize

Result: Better user experience with consistent motivation + clear next steps

modules/source/01_setup/README.md

@@ -150,4 +150,10 @@ This comprehensive module introduces:
 
 Once you've completed this module and all tests pass, you're ready to move on to the **tensor module** where you'll build the core data structures that power TinyTorch neural networks!
 
-The skills you learn here - the development workflow, testing patterns, and code organization - will be used throughout every module in TinyTorch. 
+The skills you learn here - the development workflow, testing patterns, and code organization - will be used throughout every module in TinyTorch. 
+
+## 🎉 Ready to Build?
+
+Welcome to TinyTorch! This is your foundation module where you'll master the development workflow that powers every subsequent module. You're about to build your first components and establish the coding patterns that will carry you through the entire course.
+
+Take your time, test thoroughly, and enjoy building something that really works! 🔥 

modules/source/03_activations/README.md

@@ -249,4 +249,10 @@ You've mastered this module when:
 - [ ] You can use activations in neural networks
 - [ ] You appreciate the importance of nonlinearity
 
-**Great work! You've built the mathematical foundation of neural networks!** 🎉 
+**Great work! You've built the mathematical foundation of neural networks!** 🎉 
+
+## 🎉 Ready to Build?
+
+The activations module is where neural networks come alive! You're about to implement the mathematical functions that give networks their power to learn complex patterns and make intelligent decisions.
+
+Take your time, test thoroughly, and enjoy building something that really works! 🔥

modules/source/06_cnn/README.md

@@ -67,4 +67,10 @@ python -m pytest tests/test_cnn.py -v
 
 ## 💡 Key Insight
 > **Convolution is a new, fundamental building block.**
-> By implementing it yourself, you’ll understand the magic behind modern vision models! 
+> By implementing it yourself, you’ll understand the magic behind modern vision models! 
+
+## 🎉 Ready to Build?
+
+The CNN module brings computer vision to TinyTorch! You're about to implement the core operation that powers modern image recognition, from filters and feature maps to complete convolutional networks.
+
+Take your time, test thoroughly, and enjoy building something that really works! 🔥

modules/source/09_optimizers/README.md

@@ -204,4 +204,10 @@ After mastering optimizers, you'll be ready for:
 
 **Ready to build the intelligent algorithms that power modern AI training?**
 
-Your optimizers will be the engine that transforms gradients into intelligence! 
+Your optimizers will be the engine that transforms gradients into intelligence! 
+
+## 🎉 Ready to Build?
+
+The optimizers module is where learning happens! You're about to implement the algorithms that guide neural networks toward optimal solutions, from basic gradient descent to modern adaptive methods.
+
+Take your time, test thoroughly, and enjoy building something that really works! 🔥