fix(installer): bind MSI ProductVersion to the build version

Package.wxs hardcoded Version=1.0.0.0, so every MSI ever produced claimed
ProductVersion 1.0.0.0 and MajorUpgrade could never see a newer version --
in-place upgrades silently degraded to same-version behavior. The wixproj now
derives a numeric x.y.z from $(Version) (MSI forbids prerelease suffixes in
ProductVersion) and feeds it to the WiX preprocessor.

Verified locally: Dragon-ISO-Setup-1.2.0-beta.1.msi carries ProductVersion
1.2.0.

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

installer/Dragon-ISO.Installer.wixproj

@@ -17,8 +17,17 @@
     -->
     <PublishDir>$(MSBuildThisFileDirectory)..\publish\Dragon-ISO\</PublishDir>
 
+    <!--
+      MSI ProductVersion must be numeric x.y.z (no -beta/-rc suffix), and it is
+      what MajorUpgrade compares — so it must track the real build version, not
+      a hardcoded literal. Strip any prerelease suffix from $(Version). Note:
+      two prereleases of the same x.y.z share a ProductVersion and won't
+      upgrade over each other; bump the patch digit between betas.
+    -->
+    <MsiProductVersion>$([System.Text.RegularExpressions.Regex]::Match('$(Version)', '^\d+\.\d+(\.\d+)?').Value)</MsiProductVersion>
+
     <!-- Pass MSBuild values into WiX preprocessor. -->
-    <DefineConstants>PublishDir=$(PublishDir);AssetsDir=$(MSBuildThisFileDirectory)..\src\Dragon-ISO.App\Assets\</DefineConstants>
+    <DefineConstants>PublishDir=$(PublishDir);AssetsDir=$(MSBuildThisFileDirectory)..\src\Dragon-ISO.App\Assets\;ProductVersion=$(MsiProductVersion)</DefineConstants>
 
     <!-- Code-signing hook (set externally for release builds; left empty for dev). -->
     <SignOutput Condition=" '$(SignOutput)' == '' ">false</SignOutput>

installer/Package.wxs

@@ -23,7 +23,7 @@
 
   <Package Name="Dragon-ISO"
            Manufacturer="Wild Dragon LLC"
-           Version="1.0.0.0"
+           Version="$(var.ProductVersion)"
            UpgradeCode="9F4A8B2C-1D3E-4A5B-9C6D-8E7F0A1B2C3D"
            Scope="perMachine"
            Compressed="yes"