[FEATURE] Agent view: sort by most recently updated, not just creation time

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

Agent view groups sessions by state but within each group, sessions are ordered by creation time. There's no way to sort by most recently updated. When running sessions over several days, the ones I actually care about (recently active) get buried under older sessions that happen to share the same state.

Proposed Solution

Add a sort toggle (maybe Ctrl+O or similar) to switch between "sort by created" and "sort by last updated" within each group. Alternatively, default to most-recently-updated since that's almost always what you want when scanning the list for something to act on.

Priority

Medium - Would be very helpful

Feature Category

Interactive mode (TUI) / Agent view