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/cdi.fish

@@ -1,6 +1,18 @@
 # Copyright (C) 2026 Rootiest
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
+# SYNOPSIS
+#   cdi [query]
+#
+# DESCRIPTION
+#   Alias for zi — opens zoxide's interactive directory picker for jumping to
+#   frequently-visited directories using fzf.
+#
+# ARGUMENTS
+#   query  Optional search term to pre-filter the directory list
+#
+# EXAMPLE
+#   cdi myproject
 function cdi --wraps zi --description 'Interactively jump to a directory using zoxide (alias for zi)'
     zi $argv
 end