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>

src/third_party/libsmb2/COPYING

@@ -0,0 +1,35 @@
+Libsmb2 components fall under separate licences
+
+
+The lib and include directories (except DCE/RPC)
+===============================================
+The smb2 client library itself, i.e. the lib directory and non-DCE/RPC
+headers under include/, is licenced under GNU Lesser General Public
+License as published by the Free Software Foundation; either version 2.1
+of the License, or (at your option) any later version.
+
+A copy of LGPL 2.1 is included in the file LICENCE-LGPL-2.1.txt but can
+also be downloaded from
+http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html
+
+This is the licence that applies to the libsmb2 library and its use.
+
+
+The libdcerpc directory and DCE/RPC headers
+===========================================
+The DCE/RPC library (libdcerpc/) and the DCE/RPC public headers
+(include/smb2/libsmb2-dcerpc*.h) are licenced under the 2-Clause BSD
+License.
+
+To avoid any confusion, every source file also contain a licence boilerplate.
+
+
+The examples directory
+======================
+The example applications using this library, i.e. the examples directory,
+is licenced under 2-Clause BSD License.
+
+These are executable applications that link with the libsmb2 library
+and/or libdcerpc.
+
+To avoid any confusion, every source file also contain a licence boilerplate.