docs(functions): add man-page headers to branch, fc, gitup, sudo-toggle

These four were the only documented functions with no comment header,
carrying just a one-line description. Content is merged from their manual
entries plus what the implementations actually do (fc's vi fallback and
empty-buffer abort, sudo-toggle's credential-cache clear), so the headers
are a superset of Section 5 rather than a copy of it.

functions/sudo-toggle.fish

@@ -1,3 +1,23 @@
+# Copyright (C) 2026 Rootiest
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+# CATEGORY
+#   07-system-and-monitoring
+#
+# SYNOPSIS
+#   sudo-toggle
+#
+# DESCRIPTION
+#   Toggles the sudo NOPASSWD rule on and off via
+#   /etc/sudoers.d/nofail-toggle. Useful for automated tasks that would
+#   otherwise require a password entry. Clears the sudo credential cache
+#   when re-enabling, so the lockdown takes effect immediately.
+#
+# RETURNS
+#   0  Rule toggled
+#
+# EXAMPLE
+#   sudo-toggle
 function sudo-toggle --description 'Toggle sudo password requirement on/off'
     # Check the file size using sudo stat to see if our bypass rule is active
     set -l file_size (sudo stat -c %s /etc/sudoers.d/nofail-toggle 2>/dev/null)