feat(complexity): 新增 AUTO·由模型判断 复杂度档位 (tsk_zacmwH3chZpG)

新建任务时除手选 hard/medium/easy 外，新增 AUTO 档：先以 medium 落库
占位，建任务后异步用 sonnet 起一次轻量分类调用回填三档结果并记录理由，
不阻塞建任务返回；模型不可用/解析失败一律兜底 medium，绝不报错。

- web 看板：复杂度 seg 增加第四档 AUTO（默认选中，cyan 样式），提交 complexity='auto'
- src/api/server.ts：POST tasks 接受 'auto' → medium 占位 + 异步 classify 回填（可注入 classify 测试）
- src/executor/classify.ts（新增）：buildClassifyPrompt/parseClassification/classifyComplexity
  复用 cc.ts/models.ts，sonnet 省额度，无工具、限轮限时
- src/executor/models.ts：pickClassifierModel（复用 executor easy 档 + MAESTRO_MODEL_EASY 覆盖）
- src/store/store.ts：applyAutoComplexity 回填复杂度+重置状态+理由入产出字段+广播 task.updated
- test/classify.test.ts：解析映射/兜底、prompt、回填、建任务集成（13 例）

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/store/store.ts

@@ -375,6 +375,40 @@ export class Store {
     return this.getTask(taskId)!;
   }
 
+  /**
+   * AUTO 复杂度回填：模型判定后设置任务复杂度并记录判定理由（建任务时占位 medium，此处异步回填）。
+   * - 判定档与占位不同且仍可改（COMPLEXITY_EDITABLE）→ 改复杂度 + 重置状态（同 patchTask 落位逻辑，含依赖）；
+   * - 理由写入该复杂度对应产出字段（hard→plan / medium→spec / easy→operations）的备注，仅在该字段为空时写，避免覆盖；
+   * - 始终广播 task.updated（payload 带判定档与理由），便于看板/用户复核。
+   */
+  applyAutoComplexity(taskId: string, complexity: Complexity, reason: string): Task {
+    const row = this.getTaskRow(taskId);
+    if (!row) throw new StoreError(`任务不存在: ${taskId}`);
+    const cur = row.status as TaskStatus;
+
+    let statusChange: { from: TaskStatus; to: TaskStatus } | null = null;
+    if (complexity !== row.complexity && COMPLEXITY_EDITABLE.has(cur)) {
+      const to = this.resolveReady(row, initialNextStatus(complexity));
+      this.db.prepare(`UPDATE tasks SET complexity = ?, status = ?, updated_at = ? WHERE id = ?`)
+        .run(complexity, to, now(), taskId);
+      if (to !== cur) statusChange = { from: cur, to };
+    }
+
+    // 理由写入对应产出字段（仅当为空），便于用户与执行 agent 复核
+    const field = complexity === 'hard' ? 'plan' : complexity === 'medium' ? 'spec' : 'operations';
+    const fresh = this.getTaskRow(taskId)!;
+    if (!fresh[field]) {
+      const note = `> AUTO·模型判定复杂度：${complexity}\n> 理由：${reason}`;
+      this.db.prepare(`UPDATE tasks SET ${field} = ?, updated_at = ? WHERE id = ?`).run(note, now(), taskId);
+    }
+
+    this.emit(row.project_id, taskId, 'task.updated', { auto: 'classify', complexity, reason });
+    if (statusChange) {
+      this.emit(row.project_id, taskId, 'status.changed', { ...statusChange, reason: 'complexity.auto-classified' });
+    }
+    return this.getTask(taskId)!;
+  }
+
   // ---------- 旧 todo 来源映射（sync 引擎用） ----------
   setSourceRef(taskId: string, ref: string): void {
     const row = this.getTaskRow(taskId);