Add CLAUDE.md with build, architecture, and testing guidance

[berryware]

Summary

• Adds CLAUDE.md to give Claude Code sessions immediate context without codebase exploration from scratch.
• Documents all common build/test/lint commands including per-module targeting and single-test execution.
• Explains the two-layer XML config system (cpoConfig.xml + meta XML), module responsibilities, and key class hierarchy.

What changed

New CLAUDE.md at the repo root covering:

• Build commands (full build, skip-tests, per-module, single test, Spotless, PMD, JaCoCo)
• Code quality: Spotless (Google Java Format), PMD+CPD, JaCoCo 80% minimums, license header format (non-standard [[/]] delimiters)
• Architecture: CpoAdapter hierarchy, CpoAdapterFactoryManager as singleton entry point, two-layer XML config, JDBC DataSource connection modes, cache/hot-deploy layer
• Testing: TestNG (not JUnit), Testcontainers + Docker requirement, per-database testng.xml layout
• Conventions: JAXB-generated packages, plugin-generated sources

Reviewer notes

Documentation only — no code changes.