feat(android): sync device albums with a server album

Add phone album sync to the Android client: MediaStore source (device
albums), a Room index with upload provenance, on-device previews, and a
mixed server + device album list where a linked pair collapses into a
single device card with a link indicator and mode label.

Three modes over one pipeline: A (off), B (upload copies, originals stay
local), C (upload originals and offload them locally to previews). The
sync engine tracks device changes (add/remove/rename/move/content), matches
assets to server photos by sha256 content hash, deletes only this client's
uploads, and reflects server changes without touching local originals.
Offload is automatic; the zoomed viewer pulls the server original.

Backend: expose the original content checksum in photo data (Postgres and
SQLite), additive with no migration.

Also anchor the `.gitignore` `data/` rule to `/data/` so the Android
`com.galo.android.data` package is tracked, and add the halo launcher icon.

android/README.md

@@ -100,6 +100,48 @@ While an album screen is active the client holds
 `GET /api/sse/albums/:id?token=` and backfills missed changes via
 `GET /api/albums/:id/photos?since=` after a reconnect.
 
+## Device albums and synchronization
+
+The album list mixes the server's albums with the device's own albums (MediaStore
+buckets). Each card is tagged with its source (`Сервер` / `Телефон`), and a linked
+pair shows the connection both ways: the device album shows `→ <server album>`, the
+server album shows `источник: <device albums>`.
+
+- **Access.** Enumerating device albums needs media read access: `READ_MEDIA_IMAGES`
+  and `READ_MEDIA_VIDEO` on Android 13+, or `READ_EXTERNAL_STORAGE` on Android 12
+  and lower. The app requests it at runtime; without (or with partial) access the
+  device albums are simply not shown, and server albums keep working.
+- **Synchronization modes** are chosen per device album from the album screen
+  (swipe right, or the settings icon):
+  - **Выключена (A)** — local only. Previews are generated on the device and cached
+    in the app's private cache; the album makes **no server requests**.
+  - **Копии оригиналов на сервере (B)** — originals stay on the device, copies are
+    uploaded to a chosen server album.
+  - **Перенос оригиналов на сервер (C)** — originals move to the server; the device
+    keeps previews. Freeing space replaces the original in MediaStore only after the
+    user confirms the OS write request, in batches.
+- Previews are capped at a 1600px long side (JPEG q80) and generated on the device,
+  including a poster frame for videos.
+- **Deduplication.** A device asset is matched to a server photo by the sha256 of the
+  bytes that leave the device (the server exposes each original's checksum). Content
+  already present is linked instead of re-uploaded; an edited asset is re-uploaded and
+  its previous upload removed; a pure rename is propagated via `PATCH /api/photos/:id`.
+- **Deletions.** The server photo is deleted only when this client uploaded it, its
+  content is gone from the device and no other linked album still holds it. Photos the
+  client did not upload are never touched, and a photo already gone from the server is
+  only reflected in the local index.
+- **Background.** Synchronization runs on app start and while the app is open (a
+  MediaStore content observer), and periodically in the background via WorkManager.
+  The periodic pass honors the **Только Wi-Fi** setting. Freeing space in mode C is
+  never automatic — it always waits for the user's confirmation.
+- **Provenance.** Mode C writes a marker into the EXIF of the preview it leaves
+  behind (server album/photo, original hash, mode). After a reinstall the app reads
+  these markers to restore the album link and which uploads are its own; unmarked
+  media is left alone.
+- **Reversibility.** Leaving mode C warns first and offers to fetch the originals
+  back from the server (space permitting); declining keeps previews only. Unlinking
+  an album drops the local link and never deletes photos on the server.
+
 ## Testing
 
 ```sh