[FEATURE] Pure UI optional comment field in top of session for "note to self"

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Working with many simultanious sessions at once (could be in same project or multiple projects over several vscode instances), it's hard to keep my important notes about each session in my head. Theese could be a simple as "After this sessions, remember to check xxx", or "This session lays the ground for planning XXX", or "After this sessions, run plan XXX", or "This session does XXX because XXX".
Theese are very important notes that makes the mental context switch so much easier, and improves the overall quality I can produces and produces less context-switch stress.

Proposed Solution

A single editable field (that can be expanded to a few lines with a scroller) just below the session title.
The text is stored with the session data in memory and restored if the session is restored.

Alternative Solutions

_No response_

Priority

High - Significant impact on productivity

Feature Category

Developer tools/SDK

Use Case Example

This is a typical working situation for me:

1. Start multiple concurrent Claude Code sessions in vscode (over two different projects in three different vscode windows)
2. As I monitor the sessions "Need you"' and "Decission neede" starts materialising in the various sessions
3. I switch between the sessions, but my _mental context window_ is filling up with notes about each session and start drifting
4. I have to scroll a lot to re-read session history to re-build my mental context before instructing Claude, with the danger of giving poor instructions because some om my mental notes from before has been lost

Additional Context

This is more or less a "re-opening" og the feature described in the closed #63652