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/__interactive_history_sub.fish

@@ -1,7 +1,16 @@
 # Copyright (C) 2026 Rootiest
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
-# Provides interactive history substitution using old/new pattern or sudo fallback
+# SYNOPSIS
+#   __interactive_history_sub
+#
+# DESCRIPTION
+#   Provides interactive history substitution at the prompt. When the buffer
+#   contains old/new, replaces all occurrences of 'old' with 'new' in the last
+#   history entry. When the buffer is empty, prepends 'sudo' to the last command.
+#
+# EXAMPLE
+#   # Type "foo/bar" at prompt to replace "foo" with "bar" in the last command.
 function __interactive_history_sub
     set -l current_line (commandline -b)
     set -l last_cmd $history[1]