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/dusize.fish

@@ -1,7 +1,18 @@
 # Copyright (C) 2026 Rootiest
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
-# alias dusize=du
+# SYNOPSIS
+#   dusize [dir]
+#
+# DESCRIPTION
+#   Shows a human-readable disk usage summary using du -sh. Defaults to the
+#   current directory if no argument is given.
+#
+# ARGUMENTS
+#   dir  Directory to summarize (defaults to current directory)
+#
+# EXAMPLE
+#   dusize ~/Downloads
 function dusize --wraps='du' --description 'alias dusize=du'
     du -sh (test -n "$argv[1]"; and echo $argv[1]; or echo .)
 end