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/src/app/schemas/settings.py

@@ -222,6 +222,17 @@ class ModelConnectivityTestRead(BaseModel):
     checked_at: datetime
 
 
+class SettingsCacheClearItemRead(BaseModel):
+    cacheKey: str
+    label: str
+    clearedCount: int = Field(default=0, ge=0)
+
+
+class SettingsCacheClearRead(BaseModel):
+    totalCleared: int = Field(default=0, ge=0)
+    items: list[SettingsCacheClearItemRead] = Field(default_factory=list)
+
+
 class RuntimeModelConfigRead(BaseModel):
     slot: Literal["main", "backup", "embedding", "reranker"]
     provider: str