feat: Build and release per-architecture APKs (#550)

* feat: Build and release per-architecture APKs

This commit modifies the build process to generate separate APKs for different CPU architectures (arm64-v8a, x86_64) and a universal APK. This allows for smaller, optimized downloads for users and provides specific builds for platforms like Chromebooks.

Key changes:
- In `app/build.gradle.kts`, enables ABI splits to create `arm64-v8a`, `x86_64`, and `universal` APKs during the `assembleRelease` task.
- Updates the `release.yml` GitHub Actions workflow to rename and upload each of these APKs as distinct release assets.
- Removes the previous `arm64-v8a` only filter to allow for multi-architecture builds.

* feat: Allow manual triggering of Android CI workflow

This adds the `workflow_dispatch` event to the `android-build.yml` GitHub Actions workflow.

This change enables the Android CI pipeline to be run manually from the GitHub UI, in addition to the existing triggers for pushes and pull requests.

app/build.gradle.kts

@@ -43,13 +43,20 @@ android {
                 getDefaultProguardFile("proguard-android-optimize.txt"),
                 "proguard-rules.pro"
             )
-            ndk {
-                // ARM64-only to minimize APK size (~5.8MB savings)
-                // Excludes x86_64 as emulator not needed for production builds
-                abiFilters += listOf("arm64-v8a")
-            }
         }
     }
+
+    // APK splits for GitHub releases - creates arm64, x86_64, and universal APKs
+    // AAB for Play Store handles architecture distribution automatically
+    splits {
+        abi {
+            isEnable = true
+            reset()
+            include("arm64-v8a", "x86_64")
+            isUniversalApk = true  // For F-Droid and fallback
+        }
+    }
+
     compileOptions {
         sourceCompatibility = JavaVersion.VERSION_1_8
         targetCompatibility = JavaVersion.VERSION_1_8