chore(android): bump toolchain to Gradle 9.1 + AGP 9.0.1 + Kotlin 2.2.21 for JDK 25

Original 8.x toolchain choked on the ci-android image's JDK 25 with an
opaque "25.0.3" error in `ktlintCheck`; Gradle 8.10's JDK compat matrix
caps at 23. Modern chain:

  - Gradle 9.1.0 (first to support JDK 25)
  - AGP 9.0.1 (requires Gradle 9.1+, requires Kotlin 2.2.10+)
  - Kotlin 2.2.21 / KSP 2.2.21-2.0.5 (latest 2.2.x line)
  - Compose BOM 2026.05.01 (current; pulls ui-text-google-fonts at the
    BOM-managed version, so the explicit pin was dropped)

AGP 9.0 breaking changes that affected us:
  - `kotlin-android` plugin no longer needed — AGP 9 auto-enables via
    `android.builtInKotlin=true` default. Removed alias from both the
    root build.gradle.kts and :app/build.gradle.kts.
  - `applicationVariants` API removed; we don't use it.
  - Other defaults flipped (useAndroidx, uniquePackageNames, etc.) but
    we already set them explicitly or weren't relying on the old defaults.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

android/app/build.gradle.kts

@@ -1,6 +1,9 @@
 plugins {
     alias(libs.plugins.android.application)
-    alias(libs.plugins.kotlin.android)
+    // kotlin-android removed: AGP 9.0+ auto-enables Kotlin via the
+    // android.builtInKotlin=true default. The serialization + compose-compiler
+    // plugins still need explicit application because they're language-level
+    // (Kotlin compiler) plugins beyond what built-in Kotlin provides.
     alias(libs.plugins.kotlin.serialization)
     alias(libs.plugins.compose.compiler)
     alias(libs.plugins.ksp)

android/build.gradle.kts

@@ -1,6 +1,9 @@
 plugins {
     alias(libs.plugins.android.application) apply false
-    alias(libs.plugins.kotlin.android) apply false
+    // kotlin-android plugin no longer needed: AGP 9.0+ auto-enables via
+    // android.builtInKotlin=true (default). Kept the serialization +
+    // compose-compiler plugins, which are language-level (Kotlin compiler)
+    // plugins still applied explicitly per module.
     alias(libs.plugins.kotlin.serialization) apply false
     alias(libs.plugins.ksp) apply false
     alias(libs.plugins.hilt) apply false

android/gradle/libs.versions.toml

@@ -1,10 +1,14 @@
 [versions]
-agp = "8.7.0"
-kotlin = "2.0.21"
-ksp = "2.0.21-1.0.27"
+# Pinned for JDK 25 compat: Gradle 9.1.0 supports JDK 25, AGP 9.0.1
+# requires Gradle 9.1.0+, AGP 9.0 requires Kotlin Gradle Plugin 2.2.10+,
+# KSP follows Kotlin version. See gradle-wrapper.properties for the
+# Gradle version itself.
+agp = "9.0.1"
+kotlin = "2.2.21"
+ksp = "2.2.21-2.0.5"
 hilt = "2.52"
 hilt-androidx = "1.2.0"
-compose-bom = "2024.10.01"
+compose-bom = "2026.05.01"
 nav-compose = "2.8.3"
 room = "2.6.1"
 retrofit = "2.11.0"
@@ -41,7 +45,7 @@ compose-ui-graphics = { module = "androidx.compose.ui:ui-graphics" }
 compose-ui-tooling = { module = "androidx.compose.ui:ui-tooling" }
 compose-ui-tooling-preview = { module = "androidx.compose.ui:ui-tooling-preview" }
 compose-material3 = { module = "androidx.compose.material3:material3" }
-compose-ui-text-google-fonts = { module = "androidx.compose.ui:ui-text-google-fonts", version = "1.7.5" }
+compose-ui-text-google-fonts = { module = "androidx.compose.ui:ui-text-google-fonts" }
 hilt-android = { module = "com.google.dagger:hilt-android", version.ref = "hilt" }
 hilt-compiler = { module = "com.google.dagger:hilt-compiler", version.ref = "hilt" }
 room-runtime = { module = "androidx.room:room-runtime", version.ref = "room" }

android/gradle/wrapper/gradle-wrapper.properties

@@ -1,6 +1,6 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-8.10-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-9.1.0-bin.zip
 networkTimeout=10000
 validateDistributionUrl=true
 zipStoreBase=GRADLE_USER_HOME