release: v2.12.0 — wrap event titles in week view

Bump versionName to 2.12.0 (versionCode 21200) and add the changelog.
Merging this into main triggers release.yaml, which builds, signs,
publishes and mints the v2.12.0 tag + Gitea release.

Closes #13

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 = 21102
-        versionName = "2.11.2"
+        versionCode = 21200
+        versionName = "2.12.0"
 
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
     }