docs: add Java version README, CLAUDE.md, and migration guide

Rewrite README.md for the Java branch with Maven coordinates, Java 25
badges, Neo4j/Hazelcast/Spring AI stack details, benchmark results,
and full CLI/API/MCP reference. Replace Python CLAUDE.md with Java
project instructions covering architecture, package structure, coding
conventions, and detector development. Add docs/migration-guide.md
mapping Python CLI commands, config, and APIs to their Java equivalents.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: aksOps