Update site docs and plan CLAUDE.md for plan package hardening changes

Acceptance Criteria

• plan/CLAUDE.md documents pending status in the Valid Statuses section (if not already present)
• plan/CLAUDE.md documents the --clear / empty-string attribute clearing syntax for update
• plan/CLAUDE.md documents knownSections and their aliases for work/bug/decision runes
• plan/CLAUDE.md documents the Dependencies section convention (refs in Dependencies block the next command)
• Root CLAUDE.md plan workflow section updated if any command interfaces changed
• Site docs (site/content/docs/packages/) updated if the packages index references plan package capabilities

Dependencies

• Fix plan schema bugs: pending status, severity mismatch, tag filtering — schema bug fixes
• Add source, milestone, and complexity validation to plan validate — validation gaps
• Add knownSections to Plan Rune Content Models — knownSections
• Support attribute clearing in plan CLI update command — attribute clearing

References

• Plan Package Hardening — Plan Package Hardening

Resolution

Completed: 2026-04-12

Branch: claude/spec-037-breakdown-docs-Whj40

What was done

• Updated plan/CLAUDE.md work template to include Dependencies section with ref tags
• Documented Dependencies vs References convention
• Documented known sections with aliases for work/bug/decision
• Documented attribute clearing syntax (--assignee "")
• Root CLAUDE.md was already up to date; no site doc changes needed (plan package not referenced)