Add numbered prefixes to complete modules

- Rename complete modules to numbered progression:
  - setup → 00_setup
  - tensor → 01_tensor
  - activations → 02_activations
  - layers → 03_layers
  - networks → 04_networks
  - dataloader → 05_dataloader

- Update test imports to use new numbered module names
- Keep incomplete modules (autograd, training, etc.) unnumbered
- Clear progression: 6 complete modules ready for students
- Maintains rock solid foundation approach with proper imports

modules/03_layers/layers_dev.py

@@ -36,7 +36,7 @@ This module builds on the **activations** module:
 """
 ## 📦 Where This Code Lives in the Final Package
 
-**Learning Side:** You work in `modules/layers/layers_dev.py`  
+**Learning Side:** You work in `modules/03_layers/layers_dev.py`  
 **Building Side:** Code exports to `tinytorch.core.layers`
 
 ```python

modules/03_layers/tests/test_layers.py

@@ -21,7 +21,7 @@ sys.path.insert(0, os.path.dirname(os.path.dirname(__file__)))
 from layers_dev import Dense, Tensor
 
 # Import activation functions from the activations module
-sys.path.insert(0, os.path.join(os.path.dirname(os.path.dirname(__file__)), '..', 'activations'))
+sys.path.insert(0, os.path.join(os.path.dirname(os.path.dirname(__file__)), '..', '02_activations'))
 from activations_dev import ReLU, Sigmoid, Tanh
 
 def safe_numpy(tensor):

modules/04_networks/tests/test_networks.py

@@ -20,7 +20,7 @@ from tinytorch.core.activations import ReLU, Sigmoid, Tanh
 
 # Import the networks module
 try:
-    from modules.networks.networks_dev import (
+    from modules.04_networks.networks_dev import (
         Sequential, 
         create_mlp, 
         create_classification_network,
@@ -32,7 +32,7 @@ try:
     )
 except ImportError:
     # Fallback for when module isn't exported yet
-    sys.path.append(str(project_root / "modules" / "networks"))
+    sys.path.append(str(project_root / "modules" / "04_networks"))
     from networks_dev import (
         Sequential, 
         create_mlp,