Build a Claude Code idle-notification hook

The Meridian platform team uses Claude Code and wants a local desktop notification when Claude Code emits its native Notification event with the idle_prompt notification type. The hook must run a bundled hooks/notify-idle.sh entrypoint. This requirement intentionally depends on an agent-specific event that is not in Tessl's generic event set.

Create a Tessl plugin named meridian/claude-idle-notifier under claude-idle-notifier/, ready for tessl plugin lint and tessl plugin pack.

Also create hook-decision.md in the working directory with a concise explanation of why the chosen hook tier is necessary and why the other tier cannot express this requirement. Do not modify .claude/settings.json directly.