design-and-plan skill cannot resolve shared _data/ references

[williamthorsen]

Problem

Skills reference shared _data/ files using incorrect relative paths. From a skill's base directory (e.g., ~/.claude/skills/design-and-plan/), the path _data/foo.md resolves to a nonexistent subdirectory instead of the shared ~/.claude/skills/_data/ directory. When the file can't be found, agents fall back to hardcoded behavior — recommendation rules, naming conventions, and artifact conventions are never applied.

15 of 19 skills that reference _data/ have broken paths. Only 4 (commit, create-ticket, orchestrate, review-criteria) use the correct ../_data/ prefix.

A related issue: ~/.claude/CLAUDE.md duplicates guidance that belongs in ~/.agents/AGENTS.md, and AGENTS.md itself has a broken _data/ reference.

Context

• The _data/ directory is a shared reference library installed as a sibling to skill directories
• The agents CLI (commit 424828b) was updated to install _data/ alongside skills, but existing path references were never corrected
• case-conventions.md in _data/ is unreferenced — its guidance migrated to AGENTS.md and CLAUDE.md, making the file redundant
• CLAUDE.md contains no Claude-specific guidance; its unique content (writing style examples, prompt formatting) belongs in the platform-agnostic AGENTS.md

Solution

1. Fix broken _data/ paths in 15 skill SKILL.md files: change _data/ → ../_data/; normalize backtick references to markdown links
2. Consolidate CLAUDE.md into AGENTS.md: merge unique CLAUDE.md sections into AGENTS.md, reduce CLAUDE.md to just the @~/.agents/AGENTS.md include
3. Fix AGENTS.md broken reference: replace the unresolvable markdown link on line 42 with a backtick reference
4. Delete case-conventions.md: unreferenced, redundant with AGENTS.md

Acceptance criteria

• All _data/ references in skill files use ../_data/ and markdown link syntax
• ~/.claude/CLAUDE.md contains only the AGENTS.md include directive (plus the "Read AGENTS.md" instruction)
• ~/.agents/AGENTS.md includes the writing style examples and prompt formatting section from CLAUDE.md
• AGENTS.md line 42 _data/ reference is resolvable
• case-conventions.md is deleted from content/skills/_data/
• Existing tests pass