Add status change dropdown and aggregated time estimates

Features:
- Add "Change Status" option to TaskMenu dropdown
  - Allows changing task status (backlog/in progress/blocked/done) from tree view
  - Shows current status with checkmark
  - No longer need to switch to Kanban view to change status

- Implement recursive time aggregation for subtasks
  - Tasks now show total time including all descendant subtasks
  - Display format varies based on estimates:
    - "1.5h" - only task's own estimate
    - "(2h from subtasks)" - only subtask estimates
    - "1h (3h total)" - both own and subtask estimates
  - Works in both TreeView (hierarchical) and KanbanView (flat list)
  - New utility functions: calculateTotalTime, calculateTotalTimeFlat, formatTimeWithTotal

This allows better project planning by showing total time investment for tasks with subtasks.

frontend/src/components/TreeView.jsx

@@ -14,7 +14,7 @@ import {
   updateTask,
   deleteTask
 } from '../utils/api'
-import { formatTime } from '../utils/format'
+import { formatTimeWithTotal } from '../utils/format'
 import TaskMenu from './TaskMenu'
 
 const STATUS_COLORS = {
@@ -163,13 +163,13 @@ function TaskNode({ task, projectId, onUpdate, level = 0 }) {
               </div>
 
               {/* Metadata row */}
-              {(task.estimated_minutes || (task.tags && task.tags.length > 0)) && (
+              {(formatTimeWithTotal(task) || (task.tags && task.tags.length > 0)) && (
                 <div className="flex items-center gap-3 mt-1">
                   {/* Time estimate */}
-                  {task.estimated_minutes && (
+                  {formatTimeWithTotal(task) && (
                     <div className="flex items-center gap-1 text-xs text-gray-500">
                       <Clock size={12} />
-                      <span>{formatTime(task.estimated_minutes)}</span>
+                      <span>{formatTimeWithTotal(task)}</span>
                     </div>
                   )}