config: add JetBrains Toolbox and GitHub CLI completions

- Add JetBrains Toolbox scripts directory to PATH across shells
- Initialize GitHub CLI completions in bash, fish, and PowerShell
- Lazy-load gh completions in Fish to improve startup time

home/Documents/PowerShell/Microsoft.PowerShell_profile.ps1.tmpl

@@ -85,4 +85,8 @@ function cdp { Set-Location (Get-Clipboard) }
 # Initialize completions if available
 if (Get-Command chezmoi -ErrorAction SilentlyContinue) {
     chezmoi completion powershell | Out-String | Invoke-Expression
+}
+
+if (Get-Command gh -ErrorAction SilentlyContinue) {
+    Invoke-Expression -Command $(gh completion -s powershell | Out-String)
 }