docs(functions): split RETURNS into EXIT STATUS and stdout RETURNS

RETURNS previously conflated fish's $status exit code with genuine
stdout/printed output, e.g. rm listing "0/1" as if they were print
values rather than exit codes. Rename RETURNS to EXIT STATUS across
all 83 documented functions, and reintroduce RETURNS as a distinct
label reserved for the 15 functions that actually print to stdout.

Update build-manual.py's ENTRY_HEADS to render Exit Status before
Returns, manualtools.py's SECTIONS constant, and AGENTS.md's label
order and label-usage guidance to match. Add two verify-manual.py
regression tests: EXIT STATUS bodies must never contain stray
stdout/printed language, and Returns: must always render after
Exit Status: when both are present. Regenerate docs/fish-config.md.

functions/config-help.fish

@@ -32,10 +32,14 @@
 #   -m, --man   Open the compiled man page via man -l
 #   -h, --help  Print usage and navigation reference, then exit
 #
-# RETURNS
-#   0  Manual displayed (or --help printed)
+# EXIT STATUS
+#   0  Manual displayed
 #   1  Documentation file not found, or required tool not available
 #
+# RETURNS
+#   With -h/--help, the usage and navigation reference, printed to stdout.
+#   Otherwise, the manual is shown via the resolved pager (not captured stdout).
+#
 # EXAMPLE
 #   config-help
 #   config-help keybindings