Feature request: Hook event for /clear command

Summary

Add a hook event that fires when the user runs /clear to reset the conversation.

Use Case

I use multi-project planning with progress tracking in markdown files. Currently I have:

• SessionStart hook to load planning context
• Stop hook to remind about updating progress docs

However, /clear bypasses both — it resets context without triggering SessionEnd or Stop. This means:

1. Progress tracking reminders are skipped
2. Planning context isn't reloaded after clear

Proposed Solution

Add a Clear or PreClear hook event that fires when /clear is invoked, before the context is wiped. This would allow:

• Saving state before clear
• Prompting about unsaved work
• Running cleanup tasks

Alternatively, /clear could trigger SessionEnd then SessionStart to reuse existing hooks.

Workaround

Currently none — /clear cannot be intercepted or wrapped.