feat: 提示词新增全局变量 DataDir + 触发合并/种子意图默认值调整

- prompt: 新增全局运行时变量 {{.DataDir}}(服务端数据根目录 s.m.dir),
  与 {{.Now}} 一样对所有 agent(planner/worker/mainagent/goals/chat 及自定义)可用;
  各 Vars 结构体加 DataDir 字段并在渲染时填入根 workDir,globalPromptVars 登记以便
  校验/UI 变量列表/预览识别(纯运行时变量,不入库,无需迁移)。
- trigger_merge_mode 默认 by_task→all(schema/config/后端兜底/前端初值同步)。
- seed_first_intent 默认 true→false(走标准先规划再执行);spawn_task 不再暴露该参数,
  工具建任务一律 false。

web/src/components/agent-editor.tsx

@@ -734,11 +734,11 @@ function AgentTriggersTab({ agentKey, agent }: { agentKey: string; agent?: Agent
   const [tools, setTools] = React.useState<Tool[]>([]);
   // 触发后处理策略(每 agent);初值来自 agent detail,改动即保存。
   const [runMode, setRunMode] = React.useState<"serial" | "parallel">(agent?.trigger_run_mode ?? "serial");
-  const [mergeMode, setMergeMode] = React.useState<"by_task" | "all" | "none">(agent?.trigger_merge_mode ?? "by_task");
+  const [mergeMode, setMergeMode] = React.useState<"by_task" | "all" | "none">(agent?.trigger_merge_mode ?? "all");
   const [maxParallel, setMaxParallel] = React.useState(String(agent?.trigger_max_parallel ?? 5));
   React.useEffect(() => {
     setRunMode(agent?.trigger_run_mode ?? "serial");
-    setMergeMode(agent?.trigger_merge_mode ?? "by_task");
+    setMergeMode(agent?.trigger_merge_mode ?? "all");
     setMaxParallel(String(agent?.trigger_max_parallel ?? 5));
   }, [agent?.trigger_run_mode, agent?.trigger_merge_mode, agent?.trigger_max_parallel]);