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/dot_config/fish/functions/gh.fish

@@ -0,0 +1,18 @@
+# Lazy-load gh completions on first use
+function gh --wraps gh
+    # Initialize gh completions only once
+    if not set -q __gh_initialized
+        set -g __gh_initialized 1
+
+        # Generate and source completions
+        if command -q gh
+            command gh completion -s fish | source
+        else
+            echo "gh is not installed" >&2
+            return 1
+        end
+    end
+
+    # Execute the actual gh command
+    command gh $argv
+end