重构: 后端 df-ai/commands 拆分+df-nodes/workflow 改造+P0 bug 修复

- df-ai: context 历史中毒三档自愈 sanitize_messages(AC3)+anthropic_compat tool_use_id None 跳过(AC1/AC2)+删 router/stream 死码
- df-core: events 加 select_type+decisions 多选审批契约(F-260615-01)
- df-execute: shell run_command 工具复用(F-260615-05)
- df-nodes: human_node 多选校验+2 端到端测(F-01)+取消跳 set_failed(B-03b-R1/R2/R8)
- df-workflow: executor/dag/state cancel 闭环(B-06/07/03a/b)+provider approve options(R-PD-5)
- df-storage: find_path_conflict 抽公共(R-PD-11)+COLS 常量断言
- df-ideas: 删 IdeaPromoter/PromotionPolicy 死码(R-PD-14)
- src-tauri/commands/ai: secret keyring 迁移(FR-S1/R-PD-4)+GeneratingGuard RAII+disarm(B-09/26)+newConversation 软复位(B-10)+stream 心跳/stop select/空回复判错(B-02/04/05/15)+run_command(F-05)+mask audit(AR-3)
- src-tauri/commands/{project,task,workflow,mod,lib,state}: task detail IPC(F-02)+approve decisions+task list 联动(B-29)
- Cargo.lock+Cargo.toml 依赖同步

crates/df-workflow/src/dag.rs

@@ -61,24 +61,6 @@ impl Dag {
         });
     }
 
-    /// 获取指定节点的所有上游节点 ID
-    pub fn predecessors(&self, node_id: &NodeId) -> Vec<NodeId> {
-        self.edges
-            .iter()
-            .filter(|e| &e.target == node_id)
-            .map(|e| e.source.clone())
-            .collect()
-    }
-
-    /// 获取指定节点的所有下游节点 ID
-    pub fn successors(&self, node_id: &NodeId) -> Vec<NodeId> {
-        self.edges
-            .iter()
-            .filter(|e| &e.source == node_id)
-            .map(|e| e.target.clone())
-            .collect()
-    }
-
     /// 拓扑排序 — 返回按执行顺序排列的节点 ID 层级
     ///
     /// 返回 Vec<Vec<NodeId>>，每层内的节点可以并行执行。