ci: remove Java build from automatic pipeline

User direction: stop running Java builds on every PR. Deletes:

- .github/workflows/ci-java.yml — Java CI on push/PR. Ran `mvn clean verify`
  with jacoco + spotbugs. Was firing on every PR against main and blocking
  the Go-port PR with Java-side noise.

- .github/workflows/go-parity.yml — Java-vs-Go parity test. Built the
  Java jar via `mvn package` and diffed normalized graph output against
  the Go binary. Made sense during the port but the JAR build itself
  is now off the pipeline; the test is non-runnable without it.

Kept (workflow_dispatch only, not auto-fired):
- .github/workflows/beta-java.yml
- .github/workflows/release-java.yml

These survive until Phase 6 (full destructive cutover deletes the entire
Java tree + all java workflows together).

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

Author: aksOps