Feature Request: Session-scoped compact hint / pre-configured compact note

When using /compact, there is no way to pre-configure a session-scoped hint that automatically appends to the compact summary. The only option is to manually type a note in the compact dialog each time — which is easy to forget.

Feature request:
Add a way to define a session-scoped compact hint that persists for the current session and is automatically included in every compact summary. Examples:

• A /session-note "This is a story-only session, no code changes" command
• A setting in .claude/settings.json like "compactHint": "..." that can be set per-session
• A PreCompact hook that can inject additional context into the summary

Use case:
When working in a focused session (e.g. story/documentation only, no code), the session type should survive compaction without requiring the user to remember to type it each time.