feat(packaging): desktop shortcut, icon-cache refresh, checksums, AppStream

Windows installer:
- Optional Desktop shortcut feature (default on, deselectable) via a switch to
  the WixUI_FeatureTree UI.
- Refresh the shell after install (ie4uinit -show) so .dwg/.dxf icons and
  associations appear without a reboot.
- Tidy the Add/Remove Programs entry: ARPNOREPAIR plus contact/update/comments
  metadata (Modify stays enabled for the feature tree).

Release workflow:
- Publish SHA256 sidecars for the AppImage, portable .exe, MSI and .dmg.

Linux:
- Ship an AppStream metainfo.xml for software-centre integration.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packaging/windows/main.wxs

@@ -11,6 +11,7 @@
   Provides:
     * Per-machine install under Program Files\Open CAD Studio.
     * Start Menu shortcut under Programs\Open CAD Studio.
+    * Desktop shortcut.
     * File associations for .dwg and .dxf via a single ProgID; both
       route through `OpenCADStudio.exe "%1"` so the OS hands the file
       path to the app as argv[1] (consumed in OpenCADStudio::boot).
@@ -51,6 +52,15 @@
     <Property Id='ARPPRODUCTICON' Value='AppIcon.ico' />
     <Property Id='ARPHELPLINK' Value='https://github.com/HakanSeven12/OpenCADStudio' />
     <Property Id='ARPURLINFOABOUT' Value='https://github.com/HakanSeven12/OpenCADStudio' />
+    <Property Id='ARPURLUPDATEINFO' Value='https://github.com/HakanSeven12/OpenCADStudio/releases' />
+    <Property Id='ARPCONTACT' Value='Hakan Seven' />
+    <Property Id='ARPCOMMENTS' Value='2D/3D CAD application for DWG and DXF drawings.' />
+    <!--
+      Hide "Repair" from the Apps & Features entry — there is no repair flow.
+      "Modify" is deliberately left enabled: WixUI_FeatureTree supports it, so
+      users can add/remove the optional Desktop shortcut feature later.
+    -->
+    <Property Id='ARPNOREPAIR' Value='1' />
 
     <Directory Id='TARGETDIR' Name='SourceDir'>
       <Directory Id='ProgramFiles64Folder'>
@@ -195,14 +205,66 @@
           </Component>
         </Directory>
       </Directory>
+
+      <!--
+        Desktop shortcut. A non-advertised shortcut with an explicit Target;
+        the HKCU registry value is the component KeyPath (a shortcut on its own
+        cannot be a KeyPath for a per-user resource).
+      -->
+      <Directory Id='DesktopFolder' Name='Desktop'>
+        <Component Id='DesktopShortcutComp' Guid='c5c7f1c4-3d8a-4efd-b049-4662d9143dcd'>
+          <Shortcut
+            Id='DesktopShortcut'
+            Name='Open CAD Studio'
+            Description='Launch Open CAD Studio'
+            Target='[APPLICATIONROOTDIRECTORY]OpenCADStudio.exe'
+            WorkingDirectory='APPLICATIONROOTDIRECTORY'
+            Icon='AppIcon.ico'
+            IconIndex='0' />
+          <RegistryValue
+            Root='HKCU'
+            Key='Software\Open CAD Studio'
+            Name='desktop_shortcut'
+            Type='integer'
+            Value='1'
+            KeyPath='yes' />
+        </Component>
+      </Directory>
     </Directory>
 
-    <Feature Id='Complete' Title='Open CAD Studio' Level='1'>
+    <Feature Id='Complete' Title='Open CAD Studio' Level='1' Display='expand'>
       <ComponentRef Id='MainExecutable' />
       <ComponentRef Id='DefaultPrograms' />
       <ComponentRef Id='ProgramMenuDirComp' />
+      <!-- Optional, user-deselectable in the feature tree (default on). -->
+      <Feature
+        Id='DesktopShortcut'
+        Title='Desktop shortcut'
+        Description='Add a shortcut to Open CAD Studio on the desktop.'
+        Level='1'
+        Absent='allow'>
+        <ComponentRef Id='DesktopShortcutComp' />
+      </Feature>
     </Feature>
 
+    <!--
+      Refresh the shell after install so the new .dwg / .dxf file-type icons
+      and associations appear immediately instead of only after a reboot or an
+      icon-cache rebuild. `ie4uinit -show` rebuilds the per-user icon cache.
+      Immediate execution keeps property access ([SystemFolder]); Return='ignore'
+      means it can never fail the install, and the NOT REMOVE condition skips it
+      on uninstall.
+    -->
+    <CustomAction
+      Id='RefreshShellIcons'
+      Directory='APPLICATIONROOTDIRECTORY'
+      ExeCommand='"[SystemFolder]ie4uinit.exe" -show'
+      Execute='immediate'
+      Return='ignore' />
+    <InstallExecuteSequence>
+      <Custom Action='RefreshShellIcons' After='InstallFinalize'>NOT REMOVE</Custom>
+    </InstallExecuteSequence>
+
     <!-- Installer UI + finish-screen launch checkbox (see ui.wxs). -->
     <UIRef Id='OpenCADStudioUI' />
 

packaging/windows/ui.wxs

@@ -6,7 +6,9 @@
   (which needs `-ext WixUIExtension` for the WixUI_Minimal dialog set).
 
   Provides:
-    * WixUI_Minimal wizard (Welcome → Progress → Finish).
+    * WixUI_FeatureTree wizard (Welcome → License → Features → Progress →
+      Finish). The Features page lets the user deselect the optional Desktop
+      shortcut feature (default on).
     * A pre-ticked "Launch Open CAD Studio" checkbox on the finish screen
       that starts the freshly installed exe when the user clicks Finish.
 -->
@@ -41,7 +43,7 @@
       Impersonate='yes' />
 
     <UI Id='OpenCADStudioUI'>
-      <UIRef Id='WixUI_Minimal' />
+      <UIRef Id='WixUI_FeatureTree' />
       <Publish
         Dialog='ExitDialog'
         Control='Finish'