Initial import: ESP32 ZiFi32 firmware with SMB2/3 VFS bridge

Based on https://github.com/tslabs/zx-evo/tree/master/pentevo/esp32,
extended with an SMB2/3 server that exposes the ZX Evolution's real SD
card as a network share (browse/download/upload/delete), plus assorted
stability and protocol-correctness fixes in vfs_bridge.cpp and the
vendored libsmb2 - see firmware/README.md for the detailed changelog
and current status.

Also adds:
- firmware/: ready-to-flash compiled binaries + flashing instructions
- hardware/: adapter board connection diagram, PCB photo, and Gerber
  files
- src/third_party/libsmb2: vendored from sahlberg/libsmb2 (LGPL-2.1,
  see its own COPYING/LICENCE files), de-submoduled to a plain
  snapshot with local patches applied directly

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

test/esp.py

@@ -0,0 +1,80 @@
+
+from pyftdi.spi import SpiController, SpiIOError
+from pyftdi.ftdi import Ftdi as ft
+from  binascii import hexlify
+
+# ---------------------------------------------------------------------
+
+def spix(d):
+  a = spi.exchange(d, duplex=True)
+  # print(' '.join(['{:02x}'.format(b) for b in a]))
+  return a
+
+def wr_cmd(cmd):
+# wr ESP_SPI_CMD_WR_REGS
+# wr REG_CMD
+# dummy
+# wr <cmd>
+# wr ESP_ST_IDLE
+  buf = b'\x01\x08\x00'
+  buf = buf + cmd.to_bytes(1, 'little')
+  buf = buf + b'\x00'
+  a = spix(buf)
+
+def rd_reg8(reg):
+# wr ESP_SPI_CMD_RD_REGS
+# wr <reg>
+# dummy
+# rd <data>
+  buf = b'\x02'
+  buf = buf + reg.to_bytes(1, 'little')
+  buf = buf + b'\x00\x00'
+  a = spix(buf)
+  return a[3]
+
+def rd_reg32(reg):
+# wr ESP_SPI_CMD_RD_REGS
+# wr <reg>
+# dummy
+# rd <data>
+  buf = b'\x02'
+  buf = buf + reg.to_bytes(1, 'little')
+  buf = buf + b'\x00\x00\x00\x00\x00'
+  a = spix(buf)
+  return int.from_bytes(a[3:7], 'little')
+
+def rd_dma(len):
+# wr ESP_SPI_CMD_RD_DMA
+# dummy
+# dummy
+# rd <data> ...
+  buf = b'\x04'
+  a = spi.exchange(buf, len + 3, duplex=True)
+  return a[3:]
+
+def wait_data():
+  i = 20
+  while (i):
+    if (rd_reg8(0x09) == 0x05):  # ESP_ST_DATA_S2M
+      break
+    i -= 1
+
+# ---------------------------------------------------------------------
+
+ft.show_devices()
+
+spi = SpiController()
+spi.configure('ftdi://ftdi:232h:0:1/1')
+spi = spi.get_port(cs=0, freq=14000000, mode=0)
+
+wr_cmd(0x01)          # Send GET_INFO command
+wait_data()           # Wait for data
+len = rd_reg32(0x04)  # Read data length
+print(rd_dma(len))    # Read info string
+wr_cmd(0xD0)          # Stop DMA transaction
+
+wr_cmd(0xF2)
+wait_data()
+len = rd_reg32(0x04)
+print(rd_dma(len))
+wr_cmd(0xD0)