2.18.0

Cut 2.18.0. Adds the retroactive entries for #114 and #70, whose PRs
landed on main directly rather than on this branch.

The fastlane changelog is now hand-written and capped at 500 chars —
Play rejects longer "What's New" text and F-Droid truncates it, while
copying the CHANGELOG.md section produced up to 8k chars. The sync
script keeps a committed file and only falls back to CHANGELOG.md when
one is missing.

app/build.gradle.kts

@@ -28,8 +28,8 @@ android {
         // which builds this version and then creates the matching vX.Y.Z tag +
         // release itself (versionCode is pinned to MAJOR*10000 + MINOR*100 +
         // PATCH from versionName, e.g. 2.7.2 -> 20702). See docs/RELEASING.md.
-        versionCode = 21701
-        versionName = "2.17.1"
+        versionCode = 21800
+        versionName = "2.18.0"
 
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
     }