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/drawable/ic_launcher_foreground.xml

@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Halo brand mark: a sun disc with a separated outer ring, white on brand blue.
+     Sized to sit inside the adaptive-icon safe zone (72dp of 108dp). -->
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="108dp"
+    android:height="108dp"
+    android:viewportWidth="108"
+    android:viewportHeight="108">
+    <path
+        android:fillColor="#FFFFFF"
+        android:pathData="M54,54 m-15.6,0 a15.6,15.6 0 1,0 31.2,0 a15.6,15.6 0 1,0 -31.2,0" />
+    <path
+        android:fillColor="#00000000"
+        android:strokeColor="#FFFFFF"
+        android:strokeAlpha="0.6"
+        android:strokeWidth="7.2"
+        android:pathData="M54,54 m-28.8,0 a28.8,28.8 0 1,0 57.6,0 a28.8,28.8 0 1,0 -57.6,0" />
+</vector>