feat(web): new task opens straight into chat, context rail waits for content, frosted windows

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>

web/src/lib/stores/windows.ts

@@ -94,9 +94,10 @@ export function openEntityWindow(slug: string | null): void {
 
 // Singleton "compose a new task" window — the Tasks app's New Task button
 // opens this rather than a dialog, since everything else in the desktop is
-// already a window; TaskLauncher closes it itself (via its onStarted
-// callback, wired up in WindowLayer.svelte) once the task's session window
-// takes over.
+// already a window. It renders as an empty chat (NewTaskChat, in
+// WindowLayer.svelte) sized like a real task window rather than a separate
+// compose screen, and closes itself once the task's session window takes
+// over.
 export const NEW_TASK_WINDOW_ID = 'new-task'
 
 export function openNewTaskWindow(): void {
@@ -105,7 +106,7 @@ export function openNewTaskWindow(): void {
     wm.focus(NEW_TASK_WINDOW_ID)
     return
   }
-  wm.open({ id: NEW_TASK_WINDOW_ID, title: 'New task', width: 480, height: 340, minWidth: 360, minHeight: 280 })
+  wm.open({ id: NEW_TASK_WINDOW_ID, title: 'New task', width: 900, height: 640, minWidth: 600, minHeight: 400 })
 }
 
 // Same dedupe/restore/focus pattern as openEntityWindow, for a task/session's