chore: add gradle wrapper + version catalog + root build

Bootstrapped Gradle 8.14 wrapper from HouseHoldKeaper, then upgraded
to 9.5.1 (required by AGP 9.1.1). All dependency versions verified as
latest stable on 2026-06-08, with Material 3 deliberately pinned to
1.5.0-alpha21 (Expressive APIs are not in any stable release yet).

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

gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,7 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-9.5.1-bin.zip
+networkTimeout=10000
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists