Add /add-rule skill for AI-assisted validation rules

[sunt05]

Summary

• Adds a new Claude Code skill (/add-rule) that generates Phase B validation rules from natural language descriptions
• Includes round-trip verification: AI generates code, then summarises it back in plain English so the user can compare against their original spec
• Builds on the RulesRegistry pattern from Add a draft rules registry to the validator with two test rules #1246

Motivation

See comment on #1246 for the experiment that prompted this.

Domain experts who understand SUEWS physics but don't write Python can describe rules in natural language. The skill handles code generation, test generation, and verification.

What's included

• .claude/skills/add-rule/SKILL.md — 5-step workflow (gather description, generate, verify, write, test)
• .claude/skills/add-rule/references/rule-conventions.md — coding patterns extracted from existing rules

Test plan

• Tested with stebbs_props rule spec — generated code is functionally identical to hand-written implementation
• Test with a novel rule description to verify end-to-end file writing
• Verify generated tests pass with make test-smoke

🤖 Generated with Claude Code

[github-actions]

CI Build Plan

Changed Files

No code changes detected (docs/site only or no matching paths).

Build Configuration

No code build required -- changes are docs/site/non-code only.

Rationale

• No build-triggering changes detected -> builds skipped

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