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/app/src/main/res/mipmap-anydpi-v26/ic_launcher.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8"?>
+<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
+    <background android:drawable="@color/ic_launcher_background" />
+    <foreground android:drawable="@drawable/ic_launcher_foreground" />
+    <monochrome android:drawable="@drawable/ic_launcher_foreground" />
+</adaptive-icon>