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/steam-dl.fish

@@ -1,7 +1,15 @@
 # Copyright (C) 2026 Rootiest
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
-# Run Steam while inhibiting system sleep
+# SYNOPSIS
+#   steam-dl
+#
+# DESCRIPTION
+#   Launches Steam with systemd-inhibit to prevent the system from idling
+#   or sleeping during active downloads.
+#
+# EXAMPLE
+#   steam-dl
 function steam-dl --description 'Run Steam while inhibiting system sleep'
     echo "Inhibiting sleep while Steam downloads..."
     systemd-inhibit --why="Active Download" --who="User" --what=idle:sleep steam