fix(completions): force --no-paging on bat invocations in completion scripts (#3760)

Every shell completion script (bash, zsh, fish, PowerShell) shells out
to bat to enumerate languages/themes for tab completion candidates. If
the user has wired bat into LESSOPEN (e.g. LESSOPEN='|-bat -f -pp %s'),
bat's normal pager auto-detection can engage when stdout looks like a
terminal at completion time and reflect ANSI escape sequences back into
the candidate list. The result is the issue's reproducer: tab completion
expands 'Per' to '\033[38;2;248;248;242mPerl' instead of 'Perl'.

The list-languages/list-themes calls are always meant to be machine-
readable, so they should never page. Pass --no-paging explicitly to
every bat invocation inside the four completion files. The flag is the
public alias for --paging=never (already documented in bat --help) and
is the same form completion scripts elsewhere in the codebase use.

Touches the four completion files only; no production code changes.

assets/completions/bat.bash.in

@@ -80,7 +80,7 @@ _bat() {
 	-l | --language)
 		local IFS=$'\n'
 		COMPREPLY=($(compgen -W "$(
-			"$1" --list-languages | while IFS=: read -r lang _; do
+			"$1" --no-paging --list-languages | while IFS=: read -r lang _; do
 				printf "%s\n" "$lang"
 			done
 		)" -- "$cur"))
@@ -150,14 +150,14 @@ _bat() {
 		;;
 	--theme)
 		local IFS=$'\n'
-		COMPREPLY=($(compgen -W "auto${IFS}auto:always${IFS}auto:system${IFS}dark${IFS}light${IFS}$("$1" --list-themes)" -- "$cur"))
+		COMPREPLY=($(compgen -W "auto${IFS}auto:always${IFS}auto:system${IFS}dark${IFS}light${IFS}$("$1" --no-paging --list-themes)" -- "$cur"))
 		__bat_escape_completions
 		return 0
 		;;
 	--theme-dark | \
 	--theme-light)
 		local IFS=$'\n'
-		COMPREPLY=($(compgen -W "$("$1" --list-themes)" -- "$cur"))
+		COMPREPLY=($(compgen -W "$("$1" --no-paging --list-themes)" -- "$cur"))
 		__bat_escape_completions
 		return 0
 		;;