Add Tree Ring Memory community skill

[TerminallyLazy]

Summary

• add Tree Ring Memory as a Community skill
• include DISPLAY metadata for Zo skill browsing
• document local-first install/auth behavior and agent-safe recall/remember/audit/forget/consolidate flows

Validation

• bun validate (passes; registry reports 15 pre-existing External warnings, none for Community/tree-ring-memory)
• git diff --check