calcurse: sync with Google Calendar via calcurse-caldav

Hourly timer started from xmonad, plus UI hooks that sync before load and after exit. calcurse-sync notifies once when the OAuth login expires and restarts the daemon after imports, since it never re-reads its files.

.config/calcurse/hooks/post-save

@@ -0,0 +1,6 @@
+#!/bin/sh
+# Sync the UI's saved changes once it exits (syncing while it runs would change files under it).
+[ "$(ps -o args= -p "$PPID")" = calcurse ] && [ "$(ps -o tty= -p "$PPID" | tr -d ' ')" != '?' ] || exit 0
+# shellcheck disable=SC2016 # $1 expands in the inner shell
+setsid -f sh -c 'while kill -0 "$1" 2>/dev/null; do sleep 1; done; systemctl --user start calcurse-sync.service' \
+    sh "$PPID" >/dev/null 2>&1