Android 0.16, versionCode 18

Three things landed since 0.15 was built, two of which a person will
notice.

Backups are written in the shared format now, so one made on an Android
phone opens on an iPhone and the other way round. Before this each app
sealed its own storage and refused the other's file outright, so moving
between the two lost every conversation.

A file in a chat keeps its name and its label. They reached the far end
correctly, so a received document arrived named; it was the copy kept on
this phone that lost them on the first read back out of storage, which
looks like a damaged file rather than like the app forgetting.

And an expired story's bytes are actually dropped. The history path read
every stored story back as one that never expires, so they stayed on
disk after they stopped showing.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

app/build.gradle.kts

@@ -40,8 +40,8 @@ android {
         // the paragraph above, so the code keeps climbing and the NAME is what
         // closes the 0.10 -> 0.12 gap. They are allowed to differ: the code is
         // ordering, the name is what a person reads.
-        versionCode = 17
-        versionName = "0.15"
+        versionCode = 18
+        versionName = "0.16"
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
     }