fix: PS 5.1 compat — replace non-ASCII chars in shipped PowerShell scripts (#2709)

* Initial plan

* fix: replace non-ASCII chars in PS1 files, add encoding regression tests, fix ANSI stripping in tests, update docs

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

extensions/git/commands/speckit.git.initialize.md

@@ -35,7 +35,7 @@ Replace the script to add project-specific Git initialization steps:
 ## Output
 
 On success:
-- `✓ Git repository initialized`
+- `[OK] Git repository initialized`
 
 ## Graceful Degradation
 

extensions/git/scripts/powershell/auto-commit.ps1

@@ -115,7 +115,7 @@ if (Test-Path $configFile) {
         }
     }
 } else {
-    # No config file — auto-commit disabled by default
+    # No config file -- auto-commit disabled by default
     exit 0
 }
 

extensions/git/scripts/powershell/git-common.ps1

@@ -1,6 +1,6 @@
 #!/usr/bin/env pwsh
 # Git-specific common functions for the git extension.
-# Extracted from scripts/powershell/common.ps1 — contains only git-specific
+# Extracted from scripts/powershell/common.ps1 -- contains only git-specific
 # branch validation and detection logic.
 
 function Test-HasGit {

extensions/git/scripts/powershell/initialize-repo.ps1

@@ -1,7 +1,7 @@
 #!/usr/bin/env pwsh
 # Git extension: initialize-repo.ps1
 # Initialize a Git repository with an initial commit.
-# Customizable — replace this script to add .gitignore templates,
+# Customizable -- replace this script to add .gitignore templates,
 # default branch config, git-flow, LFS, signing, etc.
 $ErrorActionPreference = 'Stop'
 
@@ -66,4 +66,4 @@ try {
     exit 1
 }
 
-Write-Host "✓ Git repository initialized"
+Write-Host "[OK] Git repository initialized"