packaging: rename app ID to org.darksingularity.OrbitHub

The reverse-DNS app ID should reflect a domain we actually control.
Renames the desktop file, AppStream metainfo, icon, Flatpak manifest,
and macOS bundle identifier from io.orbithub.OrbitHub to
org.darksingularity.OrbitHub. Also fixes a stale homepage URL in the
metainfo file pointing at an old git host.

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

CMakeLists.txt

@@ -122,7 +122,7 @@ if(APPLE)
     )
     set(MACOSX_BUNDLE_ICON_FILE orbithub.icns)
     set(MACOSX_BUNDLE_BUNDLE_NAME "OrbitHub")
-    set(MACOSX_BUNDLE_GUI_IDENTIFIER "io.orbithub.OrbitHub")
+    set(MACOSX_BUNDLE_GUI_IDENTIFIER "org.darksingularity.OrbitHub")
     set(MACOSX_BUNDLE_BUNDLE_VERSION "${PROJECT_VERSION}")
     set(MACOSX_BUNDLE_SHORT_VERSION_STRING "${PROJECT_VERSION}")
 endif()
@@ -229,15 +229,15 @@ foreach(runtime_target IN LISTS ORBITHUB_RUNTIME_TARGETS)
 endforeach()
 
 install(FILES
-    packaging/linux/io.orbithub.OrbitHub.desktop
+    packaging/linux/org.darksingularity.OrbitHub.desktop
     DESTINATION ${CMAKE_INSTALL_DATADIR}/applications
 )
 install(FILES
-    packaging/linux/io.orbithub.OrbitHub.svg
+    packaging/linux/org.darksingularity.OrbitHub.svg
     DESTINATION ${CMAKE_INSTALL_DATADIR}/icons/hicolor/scalable/apps
 )
 install(FILES
-    packaging/linux/io.orbithub.OrbitHub.metainfo.xml
+    packaging/linux/org.darksingularity.OrbitHub.metainfo.xml
     DESTINATION ${CMAKE_INSTALL_DATADIR}/metainfo
 )
 install(FILES LICENSE DESTINATION ${CMAKE_INSTALL_DATADIR}/licenses/orbithub)