A landing's menu now has a single add action, "Add lineup here", which pins
the landing and asks for the same agent at a new throw spot. The media-only
variant path (a second link between the same origin and landing), its origin
picker in the dialog, and the per-origin count badge are removed.

While placing, a live drag now draws the dashed line from the fixed end to the
cursor instead of leaving the settled line pointing at the old spot, and
repositioning a draft end publishes that hover too. Pinned ends are marked by
a rounded ring alone; the label chip is gone. The ability bar is dimmed and
inert while a landing is pinned, since only an agent can be dropped then.

Menu labels are back to short verbs, and the landing menu uses shadcn's
default spacing instead of the zeroed padding from the stack selector wrapper.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>