docs(functions): standardize all function doc blocks to UNIX man-page style

Replace all ad-hoc inline comments between license headers and function
declarations with consistent SYNOPSIS / DESCRIPTION / ARGUMENTS / RETURNS /
EXAMPLE blocks across all 99 project-owned functions/ files. No executable
logic, variable names, or exit codes were modified.

Completes Task #6 from AGENTS.md (Retroactive Function Documentation
Standardization).

functions/gitui.fish

@@ -1,7 +1,18 @@
 # Copyright (C) 2026 Rootiest
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
-# alias gitui=gitui -t mocha.ron
+# SYNOPSIS
+#   gitui [args...]
+#
+# DESCRIPTION
+#   Launches gitui with the Catppuccin Frappe theme (frappe.ron), passing any
+#   additional arguments through to the gitui command.
+#
+# ARGUMENTS
+#   args...  Arguments forwarded to the gitui command
+#
+# EXAMPLE
+#   gitui
 function gitui --wraps='gitui' --description 'alias gitui=gitui -t mocha.ron'
     command gitui -t frappe.ron $argv