feat(server): 系统缓存清理接口与 OCR 文本层兜底增强

- 新增 system_cache 模块与 POST /settings/cache/clear，管理员可一键清理 OCR 结果/运行时配置/模型失败冷却/知识库索引/地点语义等进程内缓存
- 各服务暴露 clear_*_cache 方法（ocr/runtime_settings/runtime_chat/knowledge/application_location_semantic），SettingsCacheClearRead 汇总清理项
- OCR 转图片失败时尝试用 PDF 文本层兜底构建识别文档（有效字符≥8），并写结果缓存；OcrService 暴露 clear_result_cache
- receipt_folder 车票过滤补充身份证号关键词，附件文档/操作/展示模块同步适配
- 新增 system_cache_endpoints 测试，更新 openapi_schema/ocr/receipt_folder/attachment_association_jobs 测试

server/tests/test_ocr_service.py

@@ -308,6 +308,7 @@ def test_ocr_service_rejects_pdf_ocr_when_rendered_image_fonts_are_broken(
     monkeypatch.setattr(OcrService, "_convert_pdf_to_images", fake_convert_pdf_to_images)
     monkeypatch.setattr(OcrService, "_invoke_worker", fake_invoke_worker)
     get_settings.cache_clear()
+    OcrService._result_cache.clear()
     try:
         result = OcrService().recognize_files(
             [
@@ -315,6 +316,7 @@ def test_ocr_service_rejects_pdf_ocr_when_rendered_image_fonts_are_broken(
             ]
         )
     finally:
+        OcrService._result_cache.clear()
         get_settings.cache_clear()
 
     failed = result.documents[0]
@@ -324,6 +326,63 @@ def test_ocr_service_rejects_pdf_ocr_when_rendered_image_fonts_are_broken(
     assert failed.warnings == ["PDF 转图片失败：检测到中文字体映射缺失，未生成可 OCR 的图片。"]
 
 
+def test_ocr_service_uses_pdf_text_layer_when_rendering_fails(
+    monkeypatch,
+    tmp_path: Path,
+) -> None:
+    def fake_convert_pdf_to_images(self, *, pdf_path: Path, output_dir: Path) -> tuple[list[Path], bool]:
+        raise RuntimeError("PDF 转图片失败：Missing language pack for Adobe-GB1")
+
+    def fake_invoke_worker(
+        self,
+        *,
+        python_bin: str,
+        worker_path: str,
+        input_paths: list[Path],
+    ) -> dict:
+        raise AssertionError("PDF 转图失败但文本层可用时，不应调用 OCR worker。")
+
+    monkeypatch.setenv("STORAGE_ROOT_DIR", str(tmp_path / "storage"))
+    monkeypatch.setattr(OcrService, "_resolve_python_bin", lambda self: "python")
+    monkeypatch.setattr(OcrService, "_resolve_worker_path", lambda self: "worker.py")
+    monkeypatch.setattr(OcrService, "_convert_pdf_to_images", fake_convert_pdf_to_images)
+    monkeypatch.setattr(OcrService, "_invoke_worker", fake_invoke_worker)
+    monkeypatch.setattr(
+        OcrService,
+        "_extract_pdf_text_layer",
+        lambda self, pdf_path: (
+            "G458\n"
+            "Wuhan Shanghaihongqiao\n"
+            "2026 02 20 07:55\n"
+            "票价: 354.00\n"
+            "12306 95306"
+        ),
+    )
+    get_settings.cache_clear()
+    OcrService._result_cache.clear()
+    try:
+        result = OcrService().recognize_files(
+            [
+                ("2月20_武汉-上海.pdf", b"%PDF-1.7 text-layer-fallback", "application/pdf"),
+            ]
+        )
+    finally:
+        OcrService._result_cache.clear()
+        get_settings.cache_clear()
+
+    recovered = result.documents[0]
+    assert result.success_count == 1
+    assert recovered.document_type == "train_ticket"
+    assert recovered.document_type_label == "火车/高铁票"
+    assert recovered.preview_kind == ""
+    assert recovered.preview_data_url == ""
+    assert any(field.label == "金额" and field.value == "354元" for field in recovered.document_fields)
+    assert any(field.label == "车次/航班" and field.value == "G458" for field in recovered.document_fields)
+    assert any(field.label == "行程" and field.value == "武汉-上海" for field in recovered.document_fields)
+    assert "PDF 转图片失败" in recovered.warnings[0]
+    assert "已使用 PDF 文本层" in recovered.warnings[1]
+
+
 def test_ocr_pdf_conversion_tries_next_renderer_when_poppler_font_mapping_fails(
     monkeypatch,
     tmp_path: Path,
@@ -339,6 +398,7 @@ def test_ocr_pdf_conversion_tries_next_renderer_when_poppler_font_mapping_fails(
         text: bool,
         timeout: int,
         check: bool,
+        env: dict[str, str] | None = None,
     ) -> subprocess.CompletedProcess[str]:
         calls.append(Path(command[0]).name)
         if Path(command[0]).name == "pdftoppm":
@@ -437,6 +497,7 @@ def test_ocr_service_invokes_worker_even_when_pdf_text_layer_is_usable(
         ),
     )
     get_settings.cache_clear()
+    OcrService._result_cache.clear()
     try:
         result = OcrService().recognize_files(
             [
@@ -444,6 +505,7 @@ def test_ocr_service_invokes_worker_even_when_pdf_text_layer_is_usable(
             ]
         )
     finally:
+        OcrService._result_cache.clear()
         get_settings.cache_clear()
 
     recognized = result.documents[0]