feat: implement soft delete, task editing fixes, and UI improvements

Backend:
- Add soft delete for spaces and projects (is_active flag)
- Add status_id and assignee_id to TaskUpdate schema
- Fix task PATCH endpoint to update status and assignee
- Add validation for assignee_id and status_id in task updates
- Fix health service to count tasks with "Blocked" status as blockers
- Filter out deleted spaces/projects from health dashboard
- Add workload cache invalidation on assignee changes

Frontend:
- Add delete confirmation dialogs for spaces and projects
- Fix UserSelect to display selected user name (valueName prop)
- Fix task detail modal to refresh data after save
- Enforce 2-level subtask depth limit in UI
- Fix timezone bug in date formatting (use local timezone)
- Convert NotificationBell from Tailwind to inline styles
- Add i18n translations for health, workload, settings pages
- Add parent_task_id to Task interface across components

OpenSpec:
- Archive add-delete-capability change

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/pages/Tasks.tsx

@@ -28,6 +28,7 @@ interface Task {
   start_date: string | null
   time_estimate: number | null
   subtask_count: number
+  parent_task_id: string | null
   custom_values?: CustomValueResponse[]
 }
 
@@ -83,6 +84,7 @@ export default function Tasks() {
     description: '',
     priority: 'medium',
     assignee_id: '',
+    start_date: '',
     due_date: '',
     time_estimate: '',
   })
@@ -172,6 +174,7 @@ export default function Tasks() {
             start_date: (event.data.start_date as string) ?? null,
             time_estimate: event.data.time_estimate ?? event.data.original_estimate ?? null,
             subtask_count: event.data.subtask_count ?? 0,
+            parent_task_id: (event.data.parent_task_id as string) ?? null,
           }
           return [...prev, newTask]
         })
@@ -318,8 +321,13 @@ export default function Tasks() {
       if (newTask.assignee_id) {
         payload.assignee_id = newTask.assignee_id
       }
+      if (newTask.start_date) {
+        // Convert date string to datetime format for Pydantic
+        payload.start_date = `${newTask.start_date}T00:00:00`
+      }
       if (newTask.due_date) {
-        payload.due_date = newTask.due_date
+        // Convert date string to datetime format for Pydantic
+        payload.due_date = `${newTask.due_date}T00:00:00`
       }
       if (newTask.time_estimate) {
         payload.original_estimate = Number(newTask.time_estimate)
@@ -347,6 +355,7 @@ export default function Tasks() {
         description: '',
         priority: 'medium',
         assignee_id: '',
+        start_date: '',
         due_date: '',
         time_estimate: '',
       })
@@ -419,8 +428,22 @@ export default function Tasks() {
     setSelectedTask(null)
   }
 
-  const handleTaskUpdate = () => {
-    loadData()
+  const handleTaskUpdate = async () => {
+    await loadData()
+    // If a task is selected (modal is open), re-fetch its data to show updated values
+    if (selectedTask) {
+      try {
+        const response = await api.get(`/tasks/${selectedTask.id}`)
+        const updatedTask = response.data
+        setSelectedTask({
+          ...updatedTask,
+          project_id: projectId!,
+          time_estimate: updatedTask.original_estimate,
+        })
+      } catch (err) {
+        console.error('Failed to refresh selected task:', err)
+      }
+    }
   }
 
   const handleSubtaskClick = async (subtaskId: string) => {
@@ -742,6 +765,14 @@ export default function Tasks() {
             />
             <div style={styles.fieldSpacer} />
 
+            <label style={styles.label}>{t('fields.startDate')}</label>
+            <input
+              type="date"
+              value={newTask.start_date}
+              onChange={(e) => setNewTask({ ...newTask, start_date: e.target.value })}
+              style={styles.input}
+            />
+
             <label style={styles.label}>{t('fields.dueDate')}</label>
             <input
               type="date"