/CURRENTUSER user-mode install with admin-layer drift detection

Add user-mode install support via Inno Setup's /CURRENTUSER flag:

Admin-layer drift detection (0 UAC when current):
- IsProjFSEnabled(): checks Client-ProjFS Windows optional feature
- IsEnableProjFSTaskCurrent(): queries registered task XML for hash marker
- NeedsAdminSetup(): combines both checks
- Self-elevates via /ADMINSTAGE=true only when drift detected

/CURRENTUSER mode (non-elevated):
- Deploys payload to %LocalAppData%\VFSForGit\Versions\{ver}\
- Creates Current junction + user PATH (HKCU)
- Sets GVFS_COMMON_APPDATA_ROOT and GVFS_SECURE_DATA_ROOT env vars
- Registers per-user \GVFS\AutoMount logon task

/ADMINSTAGE mode (elevated, minimal):
- Enables ProjFS feature
- Registers EnableProjFSOnAllDrives boot task from embedded XML
- Exits without deploying payload (caller handles deployment)

Build integration:
- BuildProjFSTaskXml MSBuild target generates task XML with hash marker
- Passes /DProjFSTaskXml to ISCC

System-mode (elevated) unchanged: deploys to Program Files with versioned
layout, same as Phase 2. PrivilegesRequiredOverridesAllowed=commandline
enables the /CURRENTUSER flag without changing default behavior.

Assisted-by: Claude Sonnet 4.5
Assisted-by: Claude Opus 4.6
Signed-off-by: Tyrie Vella <tyrielv@gmail.com>

Author: tyrielv

GVFS/GVFS.Installers/GVFS.Installers.csproj

@@ -3,6 +3,8 @@
   <PropertyGroup>
     <AppendTargetFrameworkToOutputPath>false</AppendTargetFrameworkToOutputPath>
     <LayoutPath>$(RepoOutPath)GVFS.Payload\bin\$(Configuration)\win-x64\</LayoutPath>
+    <ProjFSAttachScriptsDir>$(MSBuildThisFileDirectory)..\..\scripts\projfs-attach\</ProjFSAttachScriptsDir>
+    <ProjFSTaskXmlPath>$(IntermediateOutputPath)enable-projfs-on-all-drives-task.xml</ProjFSTaskXmlPath>
   </PropertyGroup>
 
   <ItemDefinitionGroup>
@@ -24,8 +26,12 @@
     <Content Include="info.bat" />
   </ItemGroup>
 
+  <Target Name="BuildProjFSTaskXml" BeforeTargets="CreateInstaller" Condition="'$(SkipCreateInstaller)' != 'true'">
+    <Exec Command='powershell.exe -NoProfile -ExecutionPolicy Bypass -File "$(ProjFSAttachScriptsDir)build-task-xml.ps1" -ScriptPath "$(ProjFSAttachScriptsDir)enable-projfs-on-all-drives.ps1" -TemplatePath "$(ProjFSAttachScriptsDir)enable-projfs-on-all-drives-task.xml.template" -OutputPath "$(ProjFSTaskXmlPath)"' />
+  </Target>
+
   <Target Name="CreateInstaller" BeforeTargets="Build" Condition="'$(SkipCreateInstaller)' != 'true'">
-    <Exec Command='"$(PkgTools_InnoSetup)\tools\ISCC.exe" /DLayoutDir="$(LayoutPath)" /DGVFSVersion=$(GVFSVersion) Setup.iss /O"$(OutputPath)"' />
+    <Exec Command='"$(PkgTools_InnoSetup)\tools\ISCC.exe" /DLayoutDir="$(LayoutPath)" /DGVFSVersion=$(GVFSVersion) /DProjFSTaskXml="$(ProjFSTaskXmlPath)" Setup.iss /O"$(OutputPath)"' />
   </Target>
 
   <Target Name="CleanInstaller" BeforeTargets="AfterClean">