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/copy.fish

@@ -1,6 +1,19 @@
 # Copyright (C) 2026 Rootiest
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
+# SYNOPSIS
+#   copy <source> <dest>
+#
+# DESCRIPTION
+#   Wrapper for cp that strips trailing slashes from source directories,
+#   preventing unwanted nested copies when the destination already exists.
+#
+# ARGUMENTS
+#   source  Source file or directory
+#   dest    Destination path
+#
+# EXAMPLE
+#   copy ./mydir/ ~/backup
 function copy
     set count (count $argv)
     if test "$count" = 2; and test -d "$argv[1]"