fix(install.ps1): trim completion banner + strip em-dash in test

Address the two cosmetic items from review:

- Completion banner middle line was 62 chars vs 59-char top/bottom borders
  (replacing the 1-char checkmark with [OK] added width that wasn't
  reflected in the trailing whitespace).  Drop 3 trailing spaces.
- Smoke test file had a single em-dash in a comment -- the only
  non-ASCII byte across both files.  Replace with -- for consistency
  with install.ps1's pure-ASCII goal.

scripts/install.ps1

@@ -1766,7 +1766,7 @@ function Start-GatewayIfConfigured {
 function Write-Completion {
     Write-Host ""
     Write-Host "+---------------------------------------------------------+" -ForegroundColor Green
-    Write-Host "|              [OK] Installation Complete!                   |" -ForegroundColor Green
+    Write-Host "|              [OK] Installation Complete!                |" -ForegroundColor Green
     Write-Host "+---------------------------------------------------------+" -ForegroundColor Green
     Write-Host ""
     

scripts/tests/test-install-ps1-stage-protocol.ps1

@@ -5,7 +5,7 @@
 #   powershell -NoProfile -ExecutionPolicy Bypass -File scripts/tests/test-install-ps1-stage-protocol.ps1
 #
 # These tests only exercise the metadata surface (-ProtocolVersion, -Manifest,
-# unknown -Stage handling).  They DO NOT actually run any install stages —
+# unknown -Stage handling).  They DO NOT actually run any install stages --
 # those have heavy side effects (winget, git clone, pip install, PATH writes)
 # and are out of scope for a unit smoke test.  All three metadata commands
 # below return without invoking Main / Invoke-AllStages.