When the user moves the cursor (up/down/home/end), the previous
cursor position briefly shows a thin accent-coloured bar (▏)
to the left of the row. Creates a subtle trail effect that makes
the new cursor position more obvious.
- Panel::prev_cursor: usize field set on every move
- Panel::cursor_flash: Option<Instant> tracks the flash
- Panel::cursor_flash_progress() returns Some(frac) for ~200ms
after each move
- cursor_up / cursor_down / cursor_home / cursor_end set the
previous position and trigger the flash
- Render path draws the bar at the previous row in accent colour
Added 1 unit test verifying prev_cursor and cursor_flash on move.
Tests: 1406 pass (was 1405), zero warnings.
vasilito
affb6690c5