feat(check): 文件要在、扫描件兜底（C10）；响应方式存进清单并可改（C12）

- check/presence.py：「提供《授权委托书》」「须提交投标函」这类要求按标题里有没有这个文件名判断，不调模型。
- 扫描件兜底：要附证明材料的要求没找到、投标文件里有扫描件页时，改为提示级「可能在扫描件里，请人工核对」。
- 响应方式解析时识别、带依据句子存进 checklist.response_modes（迁移 0008）；清单页显示、可改（写审计，
  重新解析不覆盖人工改过的）；查标用存下来的。新接口 PUT /projects/{id}/checklist/response-modes/{category}。
- check_item_result.layer 加 presence（迁移 0007）；契约同步默认接受的两种结论。

开发集 17 份：规矩投标文件的致命问题 120 → 51，致命级召回不变（22 / 32）（docs/architecture/check-eval.md §5）。

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

server/tests/test_check_units.py

@@ -131,3 +131,38 @@ def test_implicit_not_found_is_accepted_but_substantive_gets_a_hint() -> None:
     assert results[a].verdict == "implicit_accepted" and findings.spec(results[a], items[a]) is None
     spec = findings.spec(results[b], items[b])
     assert results[b].verdict == "implicit_review" and spec is not None and spec.severity == "hint"
+
+
+def test_presence_names_and_find() -> None:
+    from bid_doctor.check import presence
+
+    assert presence.names("须提供加盖公章的《法定代表人授权委托书》，否则投标无效") == ["法定代表人授权委托书"]
+    assert presence.names("投标人须提交投标函及开标一览表") == ["投标函"]
+    heading = sent(3, "4．法定代表人授权委托书")
+    body = sent(4, "本授权委托书声明：我单位授权……（这是正文里顺带提到的，很长" + "，" * 60 + "）")
+    assert presence.find("法定代表人授权委托书", [body, heading]) is heading
+    assert presence.find("营业执照", [heading]) is None
+
+
+def test_scanned_fallback_turns_missing_evidence_into_a_hint() -> None:
+    from uuid import uuid4
+
+    from bid_doctor.check import applicability
+
+    a, b = uuid4(), uuid4()
+    results = {a: match.Result("not_found", "model"), b: match.Result("not_found", "model")}
+    items = {
+        a: {"categories": ["qualification"], "title": "营业执照"},
+        b: {"categories": ["tech_param"], "title": "内存"},
+    }
+    decisions = {a: applicability.Decision(True, evidence=True), b: applicability.Decision(True)}
+    docs = [match.BidDoc(uuid4(), 1, "资格证明册", [], [12, 13])]
+    match.scanned_fallback(results, items, decisions, docs)
+    spec = findings.spec(results[a], items[a])
+    assert (
+        results[a].verdict == "scanned"
+        and spec is not None
+        and spec.severity == "hint"
+        and "2 页扫描件" in spec.explanation
+    )
+    assert results[b].verdict == "not_found"  # 技术参数不是证明材料，照常报未找到