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/Xbox/libsmb2.sln

@@ -0,0 +1,25 @@
+
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+MinimumVisualStudioVersion = 10.0.40219.1
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+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|x86 = Debug|x86
+		Release|x86 = Release|x86
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{EF73A5DF-B372-4E1C-BCB4-3DA1A4002BDD}.Debug|x86.ActiveCfg = Debug|Win32
+		{EF73A5DF-B372-4E1C-BCB4-3DA1A4002BDD}.Debug|x86.Build.0 = Debug|Win32
+		{EF73A5DF-B372-4E1C-BCB4-3DA1A4002BDD}.Release|x86.ActiveCfg = Release|Win32
+		{EF73A5DF-B372-4E1C-BCB4-3DA1A4002BDD}.Release|x86.Build.0 = Release|Win32
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {9B80C829-742C-4582-992A-ABCEAB26925E}
+	EndGlobalSection
+EndGlobal