Add YAMNet models (CPU + Edge TPU compiled) to version control

- yamnet.tflite: CPU model from Kaggle/Google (4.0MB)
- yamnet_edgetpu.tflite: compiled with edgetpu_compiler v16 (4.0MB, 32/47 ops on TPU)
- Remove .gitignore rule that excluded .tflite files

No more chasing model downloads.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -2,8 +2,7 @@
 *.ppn
 Hey-Vivi_*/
 
-# ML models (downloaded separately)
+# ML models are now tracked in git (yamnet.tflite, yamnet_edgetpu.tflite)
-models/*.tflite
 
 # Speaker voice database
 voices.db