Add session timeout indicator / remaining time display

Problem:
Amazon Q Developer chat sessions have a timeout window (estimated ~8-9 hours),
but there is no visibility into:
- When the current session started
- How much time remains before timeout
- What the actual timeout duration is

This leads to unexpected session drops mid-workflow, especially during long
automation or code generation tasks where context continuity matters.

Proposed Solution:
Add a session indicator in the Amazon Q status bar or chat panel showing:
- Session start time
- Remaining time (countdown)
- Visual warning when session is nearing expiry (e.g., <30 min)

Similar to how other AI coding tools (e.g., Claude/Cursor) display usage
and session tracking information.

Why it matters:
- Users working on multi-hour tasks (test automation, refactoring, KT sessions)
need to plan around session limits
- Losing context mid-task is disruptive — a warning would let users save
progress or wrap up before timeout
- Currently there is no API, metadata, or extension hook to build this externally

Environment:
- VS Code with Amazon Q Developer plugin
- Windows 11

The issue names no files or tests; begin at the Amazon Q status bar or chat panel and determine what session metadata the VS Code extension can access. Done means the UI shows the session start time, remaining time, timeout duration if available, and a warning before expiry, with behavior verified in the relevant extension tests.

Written by the indexing model from the issue text.