Cairn: Health Aggregator

Cairn reads your health and fitness data from the phone's health store — Apple
Health on iOS, Health Connect on Android — and saves it as plain, open-format
files (Open mHealth / IEEE 1752.1 JSON) in your own Nextcloud. You stay the sole
owner of your data: there is no central server and the developer stores nothing.

Requirements:

* Android 14 or newer. Cairn reads through Health Connect, which is part of the
system only from Android 14; on Android 8-13 it is a separate Google app from
the Play Store, which a Play-less device cannot install — so the app would
find nothing to read.
* A Nextcloud of your own is optional: without one, Cairn still reads and shows
your data, it just keeps the files on the phone.

Features:

* Reads heart rate, steps, body weight, sleep and workouts — read-only. Cairn
never writes to your health store.
* Syncs the files to your own Nextcloud over WebDAV, with optional background
sync.
* In-app dashboard with a sleep-stage deep-dive and a BMI computed from your
latest weight.
* Available in English and German.

Privacy:

* No advertising, no analytics, no trackers, no third-party services.
* Your data lives only on your device and in the Nextcloud you control — never
in any developer or third-party cloud.
* HTTPS only. The Nextcloud app password is stored in the operating system's
secure storage and can be revoked at any time.

Cairn is an aggregator and viewer, not a medical device. It makes no diagnostic
or treatment claims.

Cairn now requires Android 14 or newer. Health Connect is part of the system
only from Android 14; below that it is a separate Google app from the Play
Store, which a Play-less device cannot install — so the app could not read
anything there.

Fixed: on a phone without Health Connect, Refresh and Sync now report it
instead of spinning forever. Nextcloud connection and sync errors are shown in
German in the German app. Sleep totals no longer count time you were awake, and
the per-stage breakdown