fix(windows): handle null Path when running install.ps1 via irm | iex

When running via 'irm ccs.kaitran.ca/install.ps1 | iex', the script executes
in-memory without a file path, causing $MyInvocation.MyCommand.Path to be null.
This fix checks for null before calling Split-Path to avoid the error:
'Cannot bind argument to parameter Path because it is null'

Resolves standalone installation method detection for piped execution.

install.ps1

@@ -13,8 +13,18 @@ $ClaudeDir = "$env:USERPROFILE\.claude"
 $GlmModel = "glm-4.6"
 
 # Detect if running from git repository or standalone
-$ScriptDir = Split-Path -Parent $MyInvocation.MyCommand.Path
-$InstallMethod = if (Test-Path "$ScriptDir\ccs.ps1") { "git" } else { "standalone" }
+$ScriptDir = if ($MyInvocation.MyCommand.Path) {
+    Split-Path -Parent $MyInvocation.MyCommand.Path
+} else {
+    # Running via irm | iex (in-memory, no file path)
+    $null
+}
+
+$InstallMethod = if ($ScriptDir -and (Test-Path "$ScriptDir\ccs.ps1")) {
+    "git"
+} else {
+    "standalone"
+}
 
 # Helper Functions