CC integration: Unit test rules

[stracker-phil]

Description

Adds Claude Code developer tooling to standardize PHP unit test writing across the project.

What's included

• .claude/agents/unit-test-writer.md: A sub-agent with instructions for writing PHPUnit tests in this codebase. It includes:
  • GIVEN/WHEN/THEN doc blocks on every test method
  • A general naming convention
  • Stub-over-mock preference, with a decision table to justify mocks
  • Data providers with descriptive string keys
  • Required patterns: stateful fixture closures, testable subclasses for protected methods
  • A quality checklist the agent must verify before delivering
  • Relevant DDEV test commands
• .claude/rules/unit-test-conventions.md: A Claude Code rule scoped to tests/PHPUnit/**/*.php that instructs the assistant to always delegate test writing to the new unit-test-writer agent, never inline.
• .gitignore update: Adds general support to track relevant claude code files (include all .claude/ content, but exclude all *.local.* files in all folders).

Why

Test quality has been inconsistent - missing doc blocks, mocks where stubs suffice, no data providers, tests asserting implementation details. Routing all test work through a specialized agent with hard-wired conventions prevents regressions in test quality without requiring manual review of every test PR.