CNN v2: Add mip-level support to runtime effect

Binary format v2 includes mip_level in header (20 bytes, was 16).
Effect reads mip_level and passes to static features shader via uniform.
Shader samples from correct mip texture based on mip_level.

Changes:
- export_cnn_v2_weights.py: Header v2 with mip_level field
- cnn_v2_effect.h: Add StaticFeatureParams, mip_level member, params buffer
- cnn_v2_effect.cc: Read mip_level from weights, create/bind params buffer, update per-frame
- cnn_v2_static.wgsl: Accept params uniform, sample from selected mip level

Binary format v2:
- Header: 20 bytes (magic, version=2, num_layers, total_weights, mip_level)
- Backward compatible: v1 weights load with mip_level=0

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

1 files changed, 9 insertions, 7 deletions

diff --git a/training/export_cnn_v2_weights.py b/training/export_cnn_v2_weights.py
index 9e9e352..1086516 100755
--- a/training/export_cnn_v2_weights.py
+++ b/training/export_cnn_v2_weights.py
@@ -16,11 +16,12 @@ def export_weights_binary(checkpoint_path, output_path):
     """Export CNN v2 weights to binary format.
 
     Binary format:
-      Header (16 bytes):
+      Header (20 bytes):
         uint32 magic ('CNN2')
-        uint32 version (1)
+        uint32 version (2)
         uint32 num_layers
         uint32 total_weights (f16 count)
+        uint32 mip_level (0-3)
 
       LayerInfo × num_layers (20 bytes each):
         uint32 kernel_size
@@ -107,19 +108,20 @@ def export_weights_binary(checkpoint_path, output_path):
     print(f"  Total layers: {len(layers)}")
     print(f"  Total weights: {len(all_weights_f16)} (f16)")
     print(f"  Packed: {len(weights_u32)} u32")
-    print(f"  Binary size: {16 + len(layers) * 20 + len(weights_u32) * 4} bytes")
+    print(f"  Binary size: {20 + len(layers) * 20 + len(weights_u32) * 4} bytes")
 
     # Write binary file
     output_path = Path(output_path)
     output_path.parent.mkdir(parents=True, exist_ok=True)
 
     with open(output_path, 'wb') as f:
-        # Header (16 bytes)
-        f.write(struct.pack('<4sIII',
+        # Header (20 bytes) - version 2 with mip_level
+        f.write(struct.pack('<4sIIII',
                            b'CNN2',           # magic
-                           1,                 # version
+                           2,                 # version (bumped to 2)
                            len(layers),       # num_layers
-                           len(all_weights_f16)))  # total_weights (f16 count)
+                           len(all_weights_f16),  # total_weights (f16 count)
+                           mip_level))        # mip_level
 
         # Layer info (20 bytes per layer)
         for layer in layers: