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/_qalc_eval.fish

@@ -1,7 +1,20 @@
 # Copyright (C) 2026 Rootiest
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
-# Returns the result of a qalc calculation
+# SYNOPSIS
+#   _qalc_eval
+#
+# DESCRIPTION
+#   Reads the current commandline buffer and evaluates it as a qalc
+#   expression, printing the result. Clears the buffer and repaints
+#   after evaluation. No-ops if qalc is not installed or the buffer
+#   is empty. Intended to be bound to a key in key_bindings.fish.
+#
+# RETURNS
+#   1  qalc not found in PATH
+#
+# EXAMPLE
+#   bind \cr _qalc_eval
 function _qalc_eval
     type -q qalc || return 1