Pushes configured phone folders (DCIM, WhatsApp media, call recordings, and
so on) to a home SSH host using rsync over SSH. One-way push only, on WiFi
by default, periodic or on demand.

rsync and the SSH transport are built from source and shipped inside the
APK; nothing prebuilt is bundled. The app needs all-files access to read
arbitrary backup folders such as OEM call-recording directories.

Features:

* Incremental transfers; large videos resume (rsync --partial).
* Per-folder deletion policy: additive backup or mirror.
* Runs on unmetered WiFi, periodically or on demand.
* ed25519 key auth with strict, pinned host-key verification.
