Linux: fix taskbar pin matching and launcher icon mismatch

Add StartupWMClass=OrbitHub to the desktop file so panels (GNOME
Shell, Cinnamon, KDE) can match the running window to the pinned
launcher instead of creating a duplicate taskbar entry.

Replace the hand-authored, stale launcher SVG with PNG icons
rendered directly from createOrbitHubAppIcon() at each hicolor
theme size, so the pinned/menu icon matches the actual app icon
shown in the running window, Windows .ico, and macOS .icns.

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

CMakeLists.txt

@@ -232,10 +232,12 @@ install(FILES
     packaging/linux/org.darksingularity.OrbitHub.desktop
     DESTINATION ${CMAKE_INSTALL_DATADIR}/applications
 )
+foreach(icon_size IN ITEMS 16 24 32 48 64 128 256)
     install(FILES
-    packaging/linux/org.darksingularity.OrbitHub.svg
+        packaging/linux/icons/${icon_size}x${icon_size}/apps/org.darksingularity.OrbitHub.png
-    DESTINATION ${CMAKE_INSTALL_DATADIR}/icons/hicolor/scalable/apps
+        DESTINATION ${CMAKE_INSTALL_DATADIR}/icons/hicolor/${icon_size}x${icon_size}/apps
     )
+endforeach()
 install(FILES
     packaging/linux/org.darksingularity.OrbitHub.metainfo.xml
     DESTINATION ${CMAKE_INSTALL_DATADIR}/metainfo

packaging/linux/org.darksingularity.OrbitHub.svg

@@ -1,20 +0,0 @@
-<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 256 256">
-  <defs>
-    <linearGradient id="bg" x1="0%" y1="0%" x2="100%" y2="100%">
-      <stop offset="0%" stop-color="#20354f"/>
-      <stop offset="100%" stop-color="#0b1524"/>
-    </linearGradient>
-    <linearGradient id="ring" x1="0%" y1="0%" x2="100%" y2="0%">
-      <stop offset="0%" stop-color="#69e2ff"/>
-      <stop offset="100%" stop-color="#7cf0a3"/>
-    </linearGradient>
-  </defs>
-
-  <rect x="18" y="24" width="220" height="152" rx="16" fill="url(#bg)" stroke="#94a3b8" stroke-opacity="0.4"/>
-  <rect x="32" y="38" width="192" height="112" rx="8" fill="#101b2e"/>
-  <rect x="96" y="182" width="64" height="16" rx="8" fill="#3a4a63"/>
-  <rect x="70" y="200" width="116" height="14" rx="7" fill="#52627c"/>
-
-  <ellipse cx="128" cy="98" rx="74" ry="24" fill="none" stroke="url(#ring)" stroke-width="11" transform="rotate(-14 128 98)"/>
-  <circle cx="128" cy="98" r="18" fill="#8be4ff"/>
-</svg>