build: add kotlinx.serialization and Glance for M10

A pure-Kotlin JSON codec (so the backup round-trip test runs on the
JVM) and Jetpack Glance (the three M10 widgets). Both resolve from
google()/mavenCentral() only, no verification-metadata file exists to
update, and the repro guard checks vcsInfo/dependenciesInfo/foojay —
none of which this touches.

app/build.gradle.kts

@@ -4,6 +4,7 @@ import java.io.FileInputStream
 plugins {
     alias(libs.plugins.android.application)
     alias(libs.plugins.kotlin.compose)
+    alias(libs.plugins.kotlin.serialization)
     alias(libs.plugins.ksp)
     alias(libs.plugins.hilt)
 }
@@ -184,6 +185,12 @@ dependencies {
 
     implementation(libs.kotlinx.datetime)
     implementation(libs.kotlinx.coroutines.core)
+    implementation(libs.kotlinx.serialization.json)
+
+    // M10 home-screen widgets (docs/PLAN.md §9).
+    implementation(libs.androidx.glance.appwidget)
+    implementation(libs.androidx.glance.material3)
+
     implementation("de.jeanlucmakiola.floret:core-time")
     implementation("de.jeanlucmakiola.floret:core-locale")
     implementation("de.jeanlucmakiola.floret:core-crash")

gradle/libs.versions.toml

@@ -34,6 +34,10 @@ room = "2.8.3"
 # androidx.graphics.shapes — pulled in transitively today. M8 imports that
 # package directly, so it is declared at the version that already resolves.
 graphicsShapes = "1.0.1"
+# M10 backup: a pure-Kotlin JSON codec so BackupCodecTest runs on the JVM.
+kotlinxSerialization = "1.11.0"
+# M10 widgets.
+glance = "1.2.0"
 
 [libraries]
 # AndroidX core
@@ -112,9 +116,17 @@ androidx-room-testing = { group = "androidx.room", name = "room-testing", versio
 # Android tests - GrantPermissionRule
 androidx-test-rules = { group = "androidx.test", name = "rules", version.ref = "androidxTestRules" }
 
+# JSON — the backup codec (M10, docs/PLAN.md §7)
+kotlinx-serialization-json = { group = "org.jetbrains.kotlinx", name = "kotlinx-serialization-json", version.ref = "kotlinxSerialization" }
+
+# Glance — home-screen widgets (M10, docs/PLAN.md §9)
+androidx-glance-appwidget = { group = "androidx.glance", name = "glance-appwidget", version.ref = "glance" }
+androidx-glance-material3 = { group = "androidx.glance", name = "glance-material3", version.ref = "glance" }
+
 [plugins]
 android-application = { id = "com.android.application", version.ref = "agp" }
 android-library = { id = "com.android.library", version.ref = "agp" }
 kotlin-compose = { id = "org.jetbrains.kotlin.plugin.compose", version.ref = "kotlin" }
+kotlin-serialization = { id = "org.jetbrains.kotlin.plugin.serialization", version.ref = "kotlin" }
 ksp = { id = "com.google.devtools.ksp", version.ref = "ksp" }
 hilt = { id = "com.google.dagger.hilt.android", version.ref = "hilt" }