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。

db/schema.sql

@@ -177,13 +177,14 @@ CREATE TABLE IF NOT EXISTS exploration_nodes (
     origin         TEXT,
     owner          TEXT,
     blocked_reason TEXT,
+    delete_reason  TEXT,
     created_at     TIMESTAMPTZ NOT NULL DEFAULT now(),
     updated_at     TIMESTAMPTZ NOT NULL DEFAULT now(),
     completed_at   TIMESTAMPTZ,
     CONSTRAINT ck_node_kind CHECK (kind IN ('begin','goal','intent','fact','finding','hint','digest')),
     CONSTRAINT ck_node_state CHECK (
         (kind='begin'   AND state IN ('open')) OR
-        (kind='intent'  AND state IN ('open','running','paused','done','blocked','exhausted','stopped')) OR
+        (kind='intent'  AND state IN ('open','running','paused','done','blocked','exhausted','stopped','deleted')) OR
         (kind='goal'    AND state IN ('open','met','abandoned')) OR
         (kind='fact'    AND state IN ('confirmed','dismissed','origin')) OR
         (kind='finding' AND state IN ('confirmed','dismissed')) OR
@@ -192,6 +193,8 @@ CREATE TABLE IF NOT EXISTS exploration_nodes (
     )
 );
 ALTER TABLE exploration_nodes ADD COLUMN IF NOT EXISTS blocked_reason TEXT;
+-- 意图假删除(soft delete):state='deleted' 时,delete_reason 记用户填写的删除原因。
+ALTER TABLE exploration_nodes ADD COLUMN IF NOT EXISTS delete_reason TEXT;
 -- cold-digest (§2.3/§5.3): content_version bumps on any change that could alter a
 -- digest body (summary/state/confidence); cold_since_round stamps the planner round
 -- a node most recently went from "has a live downstream branch" to none (NULL = hot).
@@ -211,7 +214,8 @@ BEGIN
             CHECK (kind IN ('begin','goal','intent','fact','finding','hint','digest'));
     END IF;
 END $$;
--- ck_node_state: recreate when it lacks the 'paused' (older) or 'digest' (this rev) branches.
+-- ck_node_state: recreate when it lacks the 'paused' (older), 'superseded' (digest rev),
+-- or 'deleted' (intent soft-delete rev) branches.
 DO $$
 BEGIN
     IF EXISTS (
@@ -219,12 +223,13 @@ BEGIN
         WHERE conrelid='exploration_nodes'::regclass
           AND conname='ck_node_state'
           AND (pg_get_constraintdef(oid) NOT LIKE '%paused%'
-               OR pg_get_constraintdef(oid) NOT LIKE '%superseded%')
+               OR pg_get_constraintdef(oid) NOT LIKE '%superseded%'
+               OR pg_get_constraintdef(oid) NOT LIKE '%deleted%')
     ) THEN
         ALTER TABLE exploration_nodes DROP CONSTRAINT ck_node_state;
         ALTER TABLE exploration_nodes ADD CONSTRAINT ck_node_state CHECK (
             (kind='begin'   AND state IN ('open')) OR
-            (kind='intent'  AND state IN ('open','running','paused','done','blocked','exhausted','stopped')) OR
+            (kind='intent'  AND state IN ('open','running','paused','done','blocked','exhausted','stopped','deleted')) OR
             (kind='goal'    AND state IN ('open','met','abandoned')) OR
             (kind='fact'    AND state IN ('confirmed','dismissed','origin')) OR
             (kind='finding' AND state IN ('confirmed','dismissed')) OR