feat: redesign BriefingView into 3-column layout (weather · chat · news)

- Left column: weather loaded independently via /api/briefing/weather
- Center column: chat messages with input bar (unchanged behavior)
- Right column: news panel loaded from /api/briefing/news (last 2 days)
- Auto-scroll to bottom on mount and after streaming
- Background refresh also refreshes news panel
- Responsive: stacks to single column on narrow screens
- Fix TaskCard.vue to include 'cancelled' in status records

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/TaskCard.vue

@@ -20,18 +20,21 @@ const statusCycle: Record<TaskStatus, TaskStatus> = {
   todo: "in_progress",
   in_progress: "done",
   done: "todo",
+  cancelled: "todo",
 };
 
 const statusDotClass: Record<TaskStatus, string> = {
   todo: "dot-todo",
   in_progress: "dot-in-progress",
   done: "dot-done",
+  cancelled: "dot-cancelled",
 };
 
 const statusTitle: Record<TaskStatus, string> = {
   todo: "Todo — click to mark In Progress",
   in_progress: "In Progress — click to mark Done",
   done: "Done — click to mark Todo",
+  cancelled: "Cancelled — click to mark Todo",
 };
 
 function cycleStatus() {
@@ -152,6 +155,9 @@ function isOverdue(): boolean {
 .dot-done {
   background: var(--color-status-done, #22c55e);
 }
+.dot-cancelled {
+  background: var(--color-status-cancelled, #6b7280);
+}
 
 .task-title-compact {
   font-size: 0.9rem;