Add updatable ADAU1701 program via flash partition and HTTP API.

Decouple the SigmaStudio RAM download from compiled-in adau1701_program.c:
DRAD v1 blobs in the dsp partition with embedded fallback, POST /api/dsp/program,
and host-tested blob parse/serialize helpers.

Co-authored-by: Cursor <cursoragent@cursor.com>

Software/Firmware/ADAU1701-Firmware/SigmaStudioFW.h

@@ -36,19 +36,14 @@ void sigma_studio_set_device(void* i2cDevHandle);
  *
  * @param    devAddress  SigmaStudio device address (0x68 write addr).
  * @param    address     16-bit target address in DSP memory map.
- * @param    length      Payload length in bytes.
+ * @param    length      Payload length in bytes (may exceed 255).
  * @param    pData       Payload bytes.
  */
 void SIGMA_WRITE_REGISTER_BLOCK(unsigned char devAddress,
                                 unsigned int address,
-                                unsigned char length,
+                                unsigned int length,
                                 ADI_REG_TYPE* pData);
 
-/**
- * @brief    Run the DigiRadio SigmaStudio default download sequence.
- */
-void adau1701_run_default_download(void);
-
 /** Safeload data register base (0x0810..0x0814). */
 #define ADAU1701_SAFELOAD_DATA_BASE 0x0810U
 /** Safeload address register base (0x0815..0x0819). */