Add comprehensive code and test writing guides

[bernardladenthin]

Summary

This PR adds three authoritative reference documents to guide contributors on code style, test conventions, and project context:

• TEST_WRITING_GUIDE.md — Complete reference for writing JUnit 4 tests with Hamcrest assertions, data providers, mocking patterns, and editor fold organization
• CODE_WRITING_GUIDE.md — Standards for production code including named constants (DRY principle), logger injection, records for immutable types, and defensive null checks
• CLAUDE.md — Project overview, architecture, build commands, dependencies, and CI/CD guidance for AI assistants and contributors
• CODE_OF_CONDUCT.md — Contributor Covenant 2.0 code of conduct

Key Changes

• TEST_WRITING_GUIDE.md (572 lines)

  • JUnit 4 + Hamcrest assertion patterns with complete examples
  • Arrange/Act/Assert structure with // pre-assert sections
  • Data provider usage with junit-dataprovider
  • Editor fold organization by method under test
  • Test naming convention: methodUnderTest_inputOrCondition_expectedBehavior
  • Mock logger injection and LLM integration test guards
  • Anti-patterns and what NOT to do

• CODE_WRITING_GUIDE.md (167 lines)

  • Named constants requirement (DRY principle) with Javadoc
  • Constructor-based logger injection pattern
  • Records for immutable value objects
  • Defensive null/empty checks at public boundaries
  • Prompt target string constants

• CLAUDE.md (363 lines)

  • Project overview and goals
  • Build system and common Maven commands
  • Complete project structure with file descriptions
  • Core architecture (two-phase operation, key components)
  • Document format specification with header field meanings
  • Maven plugin goals and parameters
  • Testing frameworks and conventions
  • CI/CD pipeline descriptions
  • Design principles (local-first, deterministic, incremental)

• CODE_OF_CONDUCT.md (128 lines)

  • Contributor Covenant 2.0 standard code of conduct

Notable Details

• All guides include concrete code examples and anti-patterns
• Test guide emphasizes Hamcrest over JUnit assertions and editor fold organization
• Code guide enforces DRY through named constants with mandatory Javadoc
• CLAUDE.md serves as both onboarding and AI assistant context
• Guides are derived from analysis of existing codebase patterns

https://claude.ai/code/session_017t5CsBznigJ7pyVkadJg97