New Task now opens directly as an empty ChatThread (NewTaskChat) instead of
a separate compose screen, sized like a real task window. The Scope/Activity
context rail in a task window no longer renders until there's actually
something to show (touched entities, activity, or an open question),
avoiding an empty-placeholder sidebar on every new task. Also fixes the
chat input defaulting to several lines tall on window open, centers the
empty-chat greeting vertically, and gives floating windows the same
frosted-glass look as the desktop's task launcher card.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>