build(release): build the release APK for arm64-v8a only

Adds ndk.abiFilters = ["arm64-v8a"] to the release build type only, so
the release APK/AAB ship a single ABI instead of a universal build with
armeabi-v7a, x86, and x86_64. defaultConfig and the debug type are left
untouched: CI's E2E matrix runs the debug build on x86_64 emulators and
needs the x86_64 native libs (incl. libsqlcipher.so).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/build.gradle.kts

@@ -88,6 +88,14 @@ android {
             } else {
                 signingConfigs.getByName("debug")
             }
+            // Ship arm64-v8a only (issue: release-arm64-only). Scoped to this build type ONLY —
+            // do NOT move to defaultConfig or the debug type: CI's E2E matrix runs the debug build
+            // on x86_64 emulators (.github/workflows/ci.yml) and needs the x86_64 native libs
+            // (incl. libsqlcipher.so). See docs/play-compliance.md and docs/fdroid-compliance.md
+            // for the ABI-coverage tradeoff this drops (armeabi-v7a / x86 / x86_64 devices).
+            ndk {
+                abiFilters += "arm64-v8a"
+            }
         }
     }