Add index.md for ZeyBack R2RDAC project

Author: ERDALECE

org/ZeyBack/1209/2121/index.md

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+---
+name: ZeyBack R2RDAC (USB Audio / FPGA)
+project: ZeyBack
+license: GPL-3.0-or-later
+repository: https://github.com/ERDALECE/ZeyBack
+---
+
+USB Audio Class 2.0 device based on STM32H743 + FPGA.
+
+Intended use:
+- PCM up to 384 kHz / 24-bit
+- DSD (native work in progress)
+
+Notes:
+- Hardware design files are licensed under CERN-OHL-S-2.0 (see repository).
+- Third-party components (e.g., STM32Cube/HAL) retain their original licenses.