[FEATURE] Agent view should use available terminal height instead of truncating behind 'show more'

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 truncates the session list and hides entries behind a "show more" fold, even when the terminal window has plenty of vertical space to display them. On a large monitor with a tall terminal, there's significant unused whitespace below the fold. Worse, after you click into a session and come back to the list, you have to expand "show more" again every time.

Two issues:

1. The visible row count doesn't adapt to terminal height. A 60-row terminal should show more sessions than a 24-row one.
2. The "show more" state resets when you navigate away and back, so you're re-expanding it constantly.

Proposed Solution

• Dynamically size the visible list based on available terminal rows (minus the input area and any chrome). Fill the space.
• Persist the expanded state so navigating into a session and back doesn't reset the fold.

Priority

Medium - Would be very helpful

Feature Category

Interactive mode (TUI) / Agent view