Play Framework

chore: ignore Gradle build/ and .gradle/ in scaffolded apps (PF-90)

The application skeleton's .gitignore predates the Gradle migration and
was missing the two directories every gradle invocation creates at the
project root:

- /build/   — task outputs (compiled classes, jars, test reports, the
              precompiled/ tree under playPrecompile, etc.)
- /.gradle/ — project-local Gradle daemon + dependency-resolution cache.

Without these, `play new` -> `git init` would track every build artifact
on the first `git status`. Mirrors the framework repo's own .gitignore
entries (lines 33-34) so scaffolded apps and the framework agree.

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