terminal: handle minimum prompt scroll delta

Prompt scrolling negated negative deltas to count the requested jumps.
minInt(isize) has no positive signed representation, so a caller could
trigger a runtime safety panic before the search for an earlier prompt
started.

Use @abs to produce the full unsigned magnitude. An extreme negative
request now follows the normal prompt traversal and clamps at the oldest
available prompt.

src/terminal/PageList.zig

@@ -3009,7 +3009,7 @@ pub fn scroll(self: *PageList, behavior: Scroll) void {
 fn scrollPrompt(self: *PageList, delta: isize) void {
     // If we aren't jumping any prompts then we don't need to do anything.
     if (delta == 0) return;
-    const delta_start: usize = @intCast(if (delta > 0) delta else -delta);
+    const delta_start: usize = @abs(delta);
     var delta_rem: usize = delta_start;
 
     // We start at the row before or after our viewport depending on the
@@ -8833,6 +8833,16 @@ test "PageList: jump zero prompts" {
     }, s.scrollbar());
 }
 
+test "PageList: jump minimum prompt delta" {
+    const testing = std.testing;
+
+    var s = try init(testing.allocator, 10, 3, null);
+    defer s.deinit();
+
+    s.scroll(.{ .delta_prompt = std.math.minInt(isize) });
+    try testing.expectEqual(Viewport.active, s.viewport);
+}
+
 test "Screen: jump back one prompt" {
     const testing = std.testing;
     const alloc = testing.allocator;