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/cheat.fish

@@ -1,7 +1,19 @@
 # Copyright (C) 2026 Rootiest
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
-# alias cheat=cheat -c
+# SYNOPSIS
+#   cheat <topic> [args...]
+#
+# DESCRIPTION
+#   Displays colorized cheatsheets using cheat -c. Falls back to tldr, then
+#   man, if cheat is not installed.
+#
+# ARGUMENTS
+#   topic   The command or topic to look up
+#   args... Additional arguments forwarded to cheat, tldr, or man
+#
+# EXAMPLE
+#   cheat tar
 function cheat --wraps='cheat' --description 'alias cheat=cheat -c'
     if type -q cheat
         command cheat -c $argv