release: prepare v2.7.1 — privacy-respecting crash reporting

Bump committed versionCode/versionName to 2.7.1 (20701) and move the
crash-reporting entry under a 2.7.1 CHANGELOG heading. The tag remains the
source of truth; CI derives the published version from it.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/build.gradle.kts

@@ -28,8 +28,8 @@ android {
         // the tag, with versionCode = MAJOR*10000 + MINOR*100 + PATCH
         // (e.g. v2.0.0 -> 20000). These committed values are the dev/local
         // default; keep them matching the latest released tag. See docs/RELEASING.md.
-        versionCode = 20700
-        versionName = "2.7.0"
+        versionCode = 20701
+        versionName = "2.7.1"
 
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
     }