Play Framework

feat: gradle skeleton for 1.13.0 migration (PF-90)

Phase 1 of PF-90. Adds Gradle wrapper at repo root (9.5.0) and a
play-gradle-plugin scaffold at framework/gradle-plugin/. Plugin id
org.playframework.play1 with one placeholder playInfo task; subsequent
phases will add the real tasks (playRun, playTest, extractPlayModules,
playNewApp).

The framework's own Ant build (framework/build.xml) is unchanged --
Gradle and Ant coexist at repo root, with Gradle owning only the
consumer-side plugin.

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