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/paste.fish

@@ -1,7 +1,22 @@
 # Copyright (C) 2026 Rootiest
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
-# Paste from clipboard
+# SYNOPSIS
+#   paste [args...]
+#
+# DESCRIPTION
+#   Outputs clipboard contents to stdout. Uses wl-paste on Wayland,
+#   falls back to xclip on X11.
+#
+# ARGUMENTS
+#   args...  Arguments forwarded to the clipboard tool
+#
+# RETURNS
+#   0  Clipboard contents printed successfully
+#   1  No supported clipboard tool found
+#
+# EXAMPLE
+#   paste > file.txt
 function paste --description 'Paste from clipboard'
     if type -q wl-paste
         wl-paste $argv