feat(windows): set local-account creds + UK keyboard/region

- Local admin password -> "open sesame" (still a placeholder for the public repo;
  SKU pipeline must replace per-device).
- UK keyboard (InputLocale 0809) + UK region/formats (SystemLocale/UserLocale
  en-GB). Display UILanguage stays en-US because the eval media is en-US and lacks
  the en-GB display pack -- true en-GB display needs en-GB LTSC media or an injected
  language pack (future build step).

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

windows/installer/autounattend/autounattend.xml

@@ -18,10 +18,10 @@
   <settings pass="windowsPE">
     <component name="Microsoft-Windows-International-Core-WinPE" processorArchitecture="amd64"
                publicKeyToken="31bf3856ad364e35" language="neutral" versionScope="nonSxS">
-      <SetupUILanguage><UILanguage>en-GB</UILanguage></SetupUILanguage>
+      <SetupUILanguage><UILanguage>en-US</UILanguage></SetupUILanguage>
       <InputLocale>0809:00000809</InputLocale>
       <SystemLocale>en-GB</SystemLocale>
-      <UILanguage>en-GB</UILanguage>
+      <UILanguage>en-US</UILanguage>
       <UserLocale>en-GB</UserLocale>
     </component>
     <component name="Microsoft-Windows-Setup" processorArchitecture="amd64"
@@ -68,8 +68,8 @@
                publicKeyToken="31bf3856ad364e35" language="neutral" versionScope="nonSxS">
       <InputLocale>0809:00000809</InputLocale>
       <SystemLocale>en-GB</SystemLocale>
-      <UILanguage>en-GB</UILanguage>
-      <UILanguageFallback>en-GB</UILanguageFallback>
+      <UILanguage>en-US</UILanguage>
+      <UILanguageFallback>en-US</UILanguageFallback>
       <UserLocale>en-GB</UserLocale>
     </component>
     <component name="Microsoft-Windows-Shell-Setup" processorArchitecture="amd64"
@@ -88,7 +88,7 @@
             <Name>silvermetal</Name>
             <Group>Administrators</Group>
             <DisplayName>SilverMetal</DisplayName>
-            <Password><Value>SM-setup-CHANGEME-1!</Value><PlainText>true</PlainText></Password>
+            <Password><Value>open sesame</Value><PlainText>true</PlainText></Password>
           </LocalAccount>
         </LocalAccounts>
       </UserAccounts>