fix(collector): launch via Setup\CmdLine (was bypassed) + WinPE diagnostics

The boot.wim Setup\CmdLine override (legacy-Setup forcing) is authoritative over
winpeshl.ini, so it launched setup.exe directly and the collector never ran -- the
VM went straight to the old sm-bootstrap unattended install. Repoint Setup\CmdLine
at the collector (cmd /c X:\sm\Start-Collector.cmd); the collector still launches the
legacy X:\sources\setup.exe itself. Add wpeinit + an on-screen banner, and write any
collector/WinForms-load failure to X:\sm\collector-error.txt shown on the console
before falling back, so we can diagnose WinForms-in-WinPE.

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

windows/installer/build.ps1

@@ -130,8 +130,13 @@ function Invoke-ForceLegacySetup {
         Copy-Item (Join-Path $PSScriptRoot '..\collector\*') $smDir -Recurse -Force
         Copy-Item (Join-Path $smDir 'winpeshl.ini') (Join-Path $bootmnt 'Windows\System32\winpeshl.ini') -Force
         Write-Host "   staged collector to boot.wim \sm\ + winpeshl.ini"
-        $setup = if (Test-Path (Join-Path $bootmnt 'sources\setup.exe')) { 'X:\sources\setup.exe' } else { 'X:\setup.exe' }
-        $cmdline = "$setup /unattend:X:\autounattend.xml"
+        # Setup\CmdLine is the WinPE setup-image shell launch and is AUTHORITATIVE over
+        # winpeshl.ini -- point it at the SilverMetal collector so the pre-config UI runs
+        # FIRST. The collector then launches the LEGACY setup.exe itself (X:\sources\setup.exe,
+        # preserving the legacy-Setup bypass) with its generated answer file, or falls back to
+        # the default autounattend.xml on cancel/error. (Pointing Setup\CmdLine straight at
+        # setup.exe bypassed the collector entirely -- it won over winpeshl.ini.)
+        $cmdline = "cmd /c X:\sm\Start-Collector.cmd"
         $hive = Join-Path $bootmnt 'Windows\System32\config\SYSTEM'
         & reg load 'HKLM\SM_BOOT' $hive | Out-Null
         try {