A calendar for the household that nobody has to maintain

Build a calendar for the household that nobody has to maintain.

Context: Everyone living together has the same three questions: is someone home tonight,
is anyone cooking, and who is around this weekend. Right now that's answered in
a group chat, badly, four times a day.

Shared calendars exist and nobody uses them, because they demand that someone
enters things. This shouldn't. It reads from the calendars people already keep
and shows one thing: tonight, who's in and who's out.

The interface is one screen with tonight on it. Not a month view. Not events.
Just: three people home, one back late, nobody cooking.

The hard part is getting anything in without effort. Existing calendars cover
some of it, but "I'm out tonight" often isn't in anyone's calendar — it's a
thought at 4pm. So the input has to be one tap from a widget or a lock screen,
and anything more is already too much.

Second hard part: privacy inside a flat. Flatmates are not a family. Nobody
wants their whole calendar visible to the person who leaves dishes in the sink.
It has to show availability without content — "out from 7" and nothing about
what or with whom.

Works for flatshares, couples, families with teenagers. The reason existing
family apps fail is that they assume one organised person willing to run it.
Most households don't have one.

Requirements:
- Ship the smallest version that delivers the core value above, nothing more.
- Pick a stack you can deploy in a day, and state the choice before writing code.
- Handle the empty state, the error state and the offline case explicitly.
- Pricing to build toward: Free for a household of up to four — it's worthless if one flatmate won't pay
and drops out. $4/mo per household beyond that, or for the shared shopping and
chore side if that gets built later.

Start by listing the screens, then build them one at a time.