Windows: embed app icon into the executable file

The app's icon only appeared at runtime (window/taskbar), set programmatically
via QApplication::setWindowIcon(). Explorer showed the generic default icon
for orbithub.exe itself, since that requires an icon baked into the PE file
as a Windows resource at build time -- a completely separate mechanism.

Added packaging/windows/orbithub.ico, rendered directly from the same
createOrbitHubAppIcon() logic used at runtime (via a one-off export tool,
not committed) so the file icon matches what the app actually looks like.
A minimal .rc resource file embeds it, compiled in only for WIN32 builds.

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

CMakeLists.txt

@@ -78,7 +78,7 @@ set(WITH_WINPR_TOOLS OFF CACHE BOOL "" FORCE)
 
 add_subdirectory(third_party/FreeRDP EXCLUDE_FROM_ALL)
 
-add_executable(orbithub WIN32
+set(ORBITHUB_SOURCES
     src/about_dialog.cpp
     src/about_dialog.h
     src/app_icon.cpp
@@ -111,6 +111,12 @@ add_executable(orbithub WIN32
     src/unsupported_session_backend.h
 )
 
+if(WIN32)
+    list(APPEND ORBITHUB_SOURCES packaging/windows/orbithub.rc)
+endif()
+
+add_executable(orbithub WIN32 ${ORBITHUB_SOURCES})
+
 target_link_libraries(orbithub PRIVATE Qt6::Widgets Qt6::Sql)
 target_link_libraries(orbithub PRIVATE KodoTerm::KodoTerm)
 if(TARGET freerdp AND TARGET winpr)

packaging/windows/orbithub.rc

@@ -0,0 +1 @@
+1 ICON "orbithub.ico"