fix(template): Update Git for Windows to 2.54.0 + add SHA256 hash

Version 2.47.0.windows.1 no longer available on GitHub (network errors).
Updated to latest stable 2.54.0.windows.1 with SHA256 hash pinning (§1.3).

Hash: 2b96e7854f0520f0f6b709c21041d9801b1be44d5e1a0d9fa621b2fbc40f1983
Source: https://github.com/git-for-windows/git/releases

This fixes download failures in Setup-WinBuild2025 Step 11 (Tier-1 Toolchain).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

template/Setup-WinBuild2025.ps1

@@ -143,8 +143,8 @@ param(
     # Optional: if empty, DefaultPassword registry value is left as-is (Deploy may have set it).
     [string] $AdminPassword = '',
 
-    # Git for Windows version (latest LTS recommended)
-    [string] $GitVersion = '2.47.0.windows.1',
+    # Git for Windows version (latest stable)
+    [string] $GitVersion = '2.54.0.windows.1',
 
     # 7-Zip version (latest stable)
     [string] $SevenZipVersion = '24.07'
@@ -212,7 +212,7 @@ $script:Hashes = @{
 
     # Git for Windows installer from https://github.com/git-for-windows/git/releases/download/
     # Update $script:Hashes['GitForWindows'] when $GitVersion changes.
-    'GitForWindows'           = ''
+    'GitForWindows'           = '2b96e7854f0520f0f6b709c21041d9801b1be44d5e1a0d9fa621b2fbc40f1983'
 
     # 7-Zip MSI installer from https://www.7-zip.org/download.html
     # Update $script:Hashes['SevenZip'] when $SevenZipVersion changes.