Ctrl+A agents overlay can panic on narrow terminals

[EdwardTang]

When AutoDrive has just started and you press Ctrl+A to open the Agents overlay, the TUI can panic with "assertion failed: min <= max" (core::cmp).
Repro (narrow terminal):

1. Resize terminal to ~31-53 columns wide.
2. Start AutoDrive.
3. Press Ctrl+A to open Agents overlay.
   • Actual: panic at core/src/cmp.rs:1082.
   • Expected: overlay renders without crashing.

Root cause: sidebar width uses desired_sidebar.clamp(24, max_allowed) where max_allowed can be < 24 for narrow widths.

Suggested fix: guard when max_allowed < 24 and skip the clamp (use max_allowed directly).