feat: add AX620E and AX637 support (encoder NPU + decoder ONNX fallback)

feat: add board-generated audio samples, fix attn_mask bug, dp.onnx IR9

fix: remove duplicate axmodels, fix model paths, add config.json for download tracking

Inflect-Micro-v2 TTS: AX650 NPU3, U16 AXMODEL

initial commit