feat: 设置页调 batch_size + 删除任务 + /docs 去认证 + 离线模式

设置页（/settings）:
- 新增 Setting DB 模型（键值存储，持久化运行时覆盖）
- config.py 加 _apply_overrides：get_settings() 合并 DB 覆盖值
  （_applying_overrides 标志防递归：DB 初始化回调 get_settings 时不重入）
- save_setting() 写 DB + 清 lru_cache，后续任务读到新值
- settings_router.py: GET/PUT /api/settings
- settings_html.py: 设置页表单（batch_size/beam_size/sort_by_length）
  + 设备只读信息 + 保存后 reload 确认
- 验证：改 asr_batch_size=16 beam_size=1 -> 任务 ASR 日志确认生效
- 验证：重启容器后设置从 DB 恢复（持久化）

删除任务:
- task_router.py: DELETE /api/tasks/{id}，仅 done/failed 可删
  删字幕/音频/视频产物 + UploadSession + Task DB 记录
- home_html.py + history_html.py: done/failed 任务显示删除按钮
  + confirm 确认 + 调用 DELETE API + 刷新列表
- 验证：删除 task 15 成功，删除进行中 task 返回 409

/docs 去认证:
- 移除 require_docs_auth 依赖，/docs /redoc /openapi.json 直接公开

离线模式:
- Dockerfile dev/final 加 HF_HUB_OFFLINE=1 TRANSFORMERS_OFFLINE=1
  （模型已缓存在 ./models volume，无需联网验证）
- 验证：离线模式完整跑通 ASR+翻译（task 15 done）

Dockerfile

@@ -100,7 +100,9 @@ VOLUME ["/data", "/models"]
 # "Unable to load libcudnn_ops.so.9"。放在 final/dev 而非 deps，避免 ENV 变化
 # 导致 deps 的 apt/pip 层缓存失效。CPU 镜像无此目录，路径被忽略不影响。
 ENV CONFIG_PATH=/app/config.yaml \
-    LD_LIBRARY_PATH=/usr/local/lib/python3.12/site-packages/nvidia/cudnn/lib:/usr/local/lib/python3.12/dist-packages/nvidia/cudnn/lib:/usr/local/lib/python3.12/site-packages/nvidia/cublas/lib:/usr/local/lib/python3.12/dist-packages/nvidia/cublas/lib
+    LD_LIBRARY_PATH=/usr/local/lib/python3.12/site-packages/nvidia/cudnn/lib:/usr/local/lib/python3.12/dist-packages/nvidia/cudnn/lib:/usr/local/lib/python3.12/site-packages/nvidia/cublas/lib:/usr/local/lib/python3.12/dist-packages/nvidia/cublas/lib \
+    HF_HUB_OFFLINE=1 \
+    TRANSFORMERS_OFFLINE=1
 
 EXPOSE 8000
 CMD ["python", "-m", "uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000", "--reload"]
@@ -118,7 +120,9 @@ COPY config.example.yaml /app/config.example.yaml
 # 全部走 volume，镜像本身无状态、无敏感数据
 VOLUME ["/data", "/models"]
 ENV CONFIG_PATH=/app/config.yaml \
-    LD_LIBRARY_PATH=/usr/local/lib/python3.12/site-packages/nvidia/cudnn/lib:/usr/local/lib/python3.12/dist-packages/nvidia/cudnn/lib:/usr/local/lib/python3.12/site-packages/nvidia/cublas/lib:/usr/local/lib/python3.12/dist-packages/nvidia/cublas/lib
+    LD_LIBRARY_PATH=/usr/local/lib/python3.12/site-packages/nvidia/cudnn/lib:/usr/local/lib/python3.12/dist-packages/nvidia/cudnn/lib:/usr/local/lib/python3.12/site-packages/nvidia/cublas/lib:/usr/local/lib/python3.12/dist-packages/nvidia/cublas/lib \
+    HF_HUB_OFFLINE=1 \
+    TRANSFORMERS_OFFLINE=1
 
 EXPOSE 8000
 CMD ["python", "-m", "uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000"]