fix: make get-cameleer.ps1 safe under irm | iex

iex evaluates the script body in the caller's scope, so top-level
side effects leak into the user's interactive PowerShell. Two leaks
fixed:

- Dropped 'exit $LASTEXITCODE' — would close the user's shell window.
- Dropped 'Set-Location $Dir' — would leave the user sitting in
  .\installer\ after the run. install.ps1 uses $PSScriptRoot to find
  its templates, so it can be invoked from any CWD via its full path.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

get-cameleer.ps1

@@ -51,10 +51,9 @@ Write-Host ''
 Write-Host "Installer downloaded to $Dir\ — launching..."
 Write-Host ''
 
-Set-Location $Dir
+$installerPath = Join-Path $Dir 'install.ps1'
 if ($InstallerArgs) {
-    & .\install.ps1 @InstallerArgs
+    & $installerPath @InstallerArgs
 } else {
-    & .\install.ps1
+    & $installerPath
 }
-exit $LASTEXITCODE