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/ltr.fish

@@ -1,7 +1,19 @@
 # Copyright (C) 2026 Rootiest
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
-# Reversed time-sorted listing
+# SYNOPSIS
+#   ltr [args...]
+#
+# DESCRIPTION
+#   Lists all files sorted by modification time in reverse (oldest first) in
+#   long format with age-based gradient color scaling. Uses eza, falls back
+#   to lsd, then to system ls.
+#
+# ARGUMENTS
+#   args...  Arguments forwarded to the listing command
+#
+# EXAMPLE
+#   ltr ~/projects
 function ltr --description 'Reversed time-sorted listing'
     if which eza >/dev/null 2>&1
         eza --long --all --sort=modified --icons --hyperlink --color=auto --color-scale=age --color-scale-mode=gradient $argv