Add Fastmail email and calendar, multi-account neomutt

- mbsync: add Fastmail IMAP channel (rbw for credentials)
- msmtp: add Fastmail SMTP account
- neomutt: add fastmail account file, F2/F3 account switching macros
- vdirsyncer + khal: Fastmail CalDAV calendar sync
- zshrc: restore calsync alias

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

laptop/.config/khal/config

@@ -0,0 +1,12 @@
+[calendars]
+[[fastmail]]
+path = ~/.local/share/calendars/fastmail/*
+color = light blue
+
+[sqlite]
+path = ~/.local/share/khal/db.sqlite
+
+[locale]
+timeformat = %H:%M
+dateformat = %Y-%m-%d
+datetimeformat = %Y-%m-%d %H:%M