[shell-common] Add shellcheck lines for all shell files

bash/.config/bash/01_exports.bash

@@ -1,3 +1,4 @@
+# shellcheck shell=bash
 # History
 mkdir -p "${XDG_STATE_HOME}"/bash
 export HISTFILE="${XDG_STATE_HOME}"/bash/history

bash/.config/bash/10_completions.bash

@@ -1,2 +1,3 @@
+# shellcheck shell=bash
 # SSH completion based on ssh config
 [ -e "$HOME/.ssh/config" ] && complete -o "default" -o "nospace" -W "$(grep "^Host" ~/.ssh/config* | grep -v "[?*]" | cut -d " " -f2- | tr ' ' '\n')" scp sftp ssh