Session-in-progress quit dialog should identify and link to the active session

## Problem

When quitting or updating VS Code, a modal says:

> A session is in progress. Are you sure you want to quit?

The dialog does not identify which session is running or provide a way to locate it. This makes the warning difficult to trust, especially when the user was not aware that a session was still active and cannot find it.

The prompt can also appear in the Agents window and across open editor windows, requiring the user to dismiss it repeatedly.

## Expected behavior

The confirmation should:

- identify the running session (for example, by title and workspace/repository), and
- provide an action to open or reveal that session.

Ideally, quitting/updating should use a single confirmation rather than prompting independently in multiple windows.

## Actual behavior

The dialog only offers **Cancel** and **Quit** without enough context to make an informed choice, and it may require interaction in each open window.

Start by tracing the quit/update confirmation used by the Agents window and open editor windows. Determine how the active session can be identified and revealed, then verify that one informative confirmation replaces repeated prompts and still supports Cancel and Quit.

Written by the indexing model from the issue text.