feat(intent): 意图删除支持假删除/真删除两种模式

删除入口区分两种模式(待领/运行中/已暂停的意图均可删除):

- 假删除(默认):意图置 state='deleted'、删除原因记入新字段 delete_reason,
  保留节点与全部产出/血缘,不再在图上另挂 fact。
- 真删除:物理删除意图及「仅由它支撑」的独占子孙(沿 yields/derived_from
  级联到叶子),避免孤立数据;共享节点、目标、任务根事实保留。被删意图先做
  token rollup 并清理 activity/副会话,被删 finding 先删 findings 行。

两种模式都照常用 cancelled 触发通知 planner(带删除前捕获的意图摘要 + 原因),
planner 文案不再声称原因挂为事实。

- DB: 新增 SoftDeleteIntent、重写 CancelIntent 为深度独占级联;schema 加
  delete_reason 列与 intent 的 deleted 状态(含旧库迁移)。
- 前端: 删除对话框加模式切换与动态说明,状态徽章/图标新增「已删除」,
  播报板展开展示删除原因。

server/manager.go

@@ -1838,11 +1838,13 @@ func (t *Task) NotifyGoalEdited(oldText, newText string) {
 
 // NotifyCancelled records that the human deleted intentID (reason = 删除原因), then
 // wakes the planner so the next round spells out which intent was removed and why.
-// The intent is stopped (not deleted); the reason is attached to it as a fact.
-func (t *Task) NotifyCancelled(intentID int64, reason string) {
+// summary is the intent's text captured before deletion — needed for hard delete,
+// where the node is gone by the time the planner reads the trigger. Applies to both
+// soft (state='deleted') and hard (physical cascade) delete.
+func (t *Task) NotifyCancelled(intentID int64, summary, reason string) {
 	if intentID > 0 {
 		t.trigMu.Lock()
-		t.pendingTriggers = append(t.pendingTriggers, agent.TriggerEvent{Kind: "cancelled", IntentID: intentID, Detail: reason})
+		t.pendingTriggers = append(t.pendingTriggers, agent.TriggerEvent{Kind: "cancelled", IntentID: intentID, Summary: summary, Detail: reason})
 		t.trigMu.Unlock()
 	}
 	t.Notify()