feat(cnn_v3): upgrade architecture to enc_channels=[8,16]

Double encoder capacity: enc0 4→8ch, enc1 8→16ch, bottleneck 16→16ch,
dec1 32→8ch, dec0 16→4ch. Total weights 2476→7828 f16 (~15.3 KB).
FiLM MLP output 40→72 params (L1: 16×40→16×72).

16-ch textures split into _lo/_hi rgba32uint pairs (enc1, bottleneck).
enc0 and dec1 textures changed from rgba16float to rgba32uint (8ch).
GBUF_RGBA32UINT node gains CopySrc for parity test readback.

- WGSL shaders: all 5 passes rewritten for new channel counts
- C++ CNNv3Effect: new weight offsets/sizes, 8ch uniform structs
- Web tool (shaders.js + tester.js): matching texture formats and bindings
- Parity test: readback_rgba32uint_8ch helper, updated vector counts
- Training scripts: default enc_channels=[8,16], updated docstrings
- Docs + architecture PNG regenerated

handoff(Gemini): CNN v3 [8,16] upgrade complete. All code, tests, web
tool, training scripts, and docs updated. Next: run training pass.

1 files changed, 9 insertions, 9 deletions

diff --git a/cnn_v3/docs/gen_architecture_png.py b/cnn_v3/docs/gen_architecture_png.py
index bd60a97..1c2ff65 100644
--- a/cnn_v3/docs/gen_architecture_png.py
+++ b/cnn_v3/docs/gen_architecture_png.py
@@ -108,20 +108,20 @@ def dim_label(x, y, txt):
 box(EX, Y_IN,  BW, BH_IO, C_IO,   'G-Buffer Features',
     '20 channels  ·  full res')
 
-box(EX, Y_E0,  BW, BH,    C_ENC,  'enc0  Conv(20→4, 3×3) + FiLM + ReLU',
-    'full res  ·  4 ch')
+box(EX, Y_E0,  BW, BH,    C_ENC,  'enc0  Conv(20→8, 3×3) + FiLM + ReLU',
+    'full res  ·  8 ch')
 
-box(EX, Y_E1,  BW, BH,    C_ENC,  'enc1  Conv(4→8, 3×3) + FiLM + ReLU',
-    '½ res  ·  8 ch  ·  (AvgPool↓ on input)')
+box(EX, Y_E1,  BW, BH,    C_ENC,  'enc1  Conv(8→16, 3×3) + FiLM + ReLU',
+    '½ res  ·  16 ch  ·  (AvgPool↓ on input)')
 
 box(BX, Y_BN,  BW_BN, BH_BN, C_BN,
-    'bottleneck  Conv(8→8, 3×3, dilation=2) + ReLU',
-    '¼ res  ·  8 ch  ·  no FiLM  ·  effective RF ≈ 10 px @ ½res')
+    'bottleneck  Conv(16→16, 3×3, dilation=2) + ReLU',
+    '¼ res  ·  16 ch  ·  no FiLM  ·  effective RF ≈ 10 px @ ½res')
 
-box(DX, Y_D1,  BW, BH,    C_DEC,  'dec1  Conv(16→4, 3×3) + FiLM + ReLU',
-    '½ res  ·  4 ch  ·  (upsample↑ + cat enc1 skip)')
+box(DX, Y_D1,  BW, BH,    C_DEC,  'dec1  Conv(32→8, 3×3) + FiLM + ReLU',
+    '½ res  ·  8 ch  ·  (upsample↑ + cat enc1 skip)')
 
-box(DX, Y_D0,  BW, BH,    C_DEC,  'dec0  Conv(8→4, 3×3) + FiLM + sigmoid',
+box(DX, Y_D0,  BW, BH,    C_DEC,  'dec0  Conv(16→4, 3×3) + FiLM + sigmoid',
     'full res  ·  4 ch  ·  (upsample↑ + cat enc0 skip)')
 
 box(DX, Y_OUT, BW, BH_IO, C_IO,   'RGBA Output',