feat(api): 实验归档支持批量删除（含缺失项如实回报）

「实验对比」页需要批量删除，逐个 DELETE 会有 N 次往返且中途失败会留下半删除状态。

- `POST /experiments/bulk-delete`：一次最多 200 个 id（`BULK_DELETE_MAX_IDS`），
  按请求顺序去重；返回 `deleted` / `missing` / `count`，**存在的删掉、不存在的如实列出**，
  不假装全部成功（前端据此提示「N 个已删、M 个不存在」）。
- 路由声明在 `GET /{experiment_id}` 之前，避免被路径参数吞掉。
- 测试 +2：删除与缺失混合场景、id 列表校验（空/超长）。

backend/tests/test_jobs_experiments.py

@@ -6,9 +6,11 @@ import sys
 from datetime import date, datetime
 
 import pytest
+from app.api.experiments import BULK_DELETE_MAX_IDS
 from app.application.services import job_executor as je
 from app.application.services.job_executor import execute_job
 from app.domain.entities.research import (
+    ExperimentRecord,
     JobRecord,
     JobStatus,
     ResearchSpec,
@@ -266,6 +268,53 @@ class TestJobsApi:
         with TestClient(app) as client:
             assert client.get("/api/jobs/JOB-NOPE").status_code == 404
 
+    def test_bulk_delete_reports_deleted_and_missing(self, seeded_api_db) -> None:
+        """批量删除：成功 / 库里没有的 id **分开回报**，且真的从列表里消失。
+
+        为什么坚持分开回报：把「没找到」也算成功，界面上就会显示「已删除 4 个」
+        而实际只删了 2 个 —— 用户下次刷新发现还在，却查不出原因。
+        """
+        spec_json = _spec().model_dump_json()
+        with sess_mod.SessionLocal() as session:
+            repo = SqlAlchemyExperimentRepository(session)
+            for eid in ("EXP-A", "EXP-B"):
+                repo.save(
+                    ExperimentRecord(
+                        id=eid,
+                        kind="backtest",
+                        spec_json=spec_json,
+                        result_json="{}",
+                        summary_text="自检用",
+                        created_at=datetime(2026, 10, 1, 10, 0, 0),
+                    )
+                )
+            session.commit()
+
+        with TestClient(app) as client:
+            # 重复 id 只算一次（EXP-A 出现两次）
+            resp = client.post(
+                "/api/experiments/bulk-delete",
+                json={"ids": ["EXP-A", "EXP-B", "EXP-A", "EXP-NOPE"]},
+            )
+            assert resp.status_code == 200
+            body = resp.json()
+            assert body["deleted"] == ["EXP-A", "EXP-B"]
+            assert body["missing"] == ["EXP-NOPE"]
+            assert body["count"] == 2
+            left = {e["id"] for e in client.get("/api/experiments").json()}
+            assert not ({"EXP-A", "EXP-B"} & left)
+
+    def test_bulk_delete_validates_ids(self, seeded_api_db) -> None:
+        """空列表 / 超上限 / 缺字段一律 422（不静默截断成前 N 个）。"""
+        with TestClient(app) as client:
+            assert client.post("/api/experiments/bulk-delete", json={"ids": []}).status_code == 422
+            assert client.post("/api/experiments/bulk-delete", json={}).status_code == 422
+            too_many = [f"EXP-{i}" for i in range(BULK_DELETE_MAX_IDS + 1)]
+            resp = client.post("/api/experiments/bulk-delete", json={"ids": too_many})
+            assert resp.status_code == 422
+            # 错误里必须写清上限，用户才知道要分几批
+            assert str(BULK_DELETE_MAX_IDS) in resp.text
+
     def test_experiments_list_and_detail(self, seeded_api_db) -> None:
         with TestClient(app) as client:
             # 先跑一个 job 生成归档，再验证列表与详情