feat：新增大屏存取发布接口

app/api/public.py

@@ -0,0 +1,54 @@
+"""匿名接口，统一放在 /api/public 下，一眼能看出哪些不鉴权"""
+
+from typing import Any
+
+from fastapi import APIRouter
+from fastapi.responses import FileResponse
+
+from app.api.screens import Service
+from app.common.response import ApiResponse, success_response
+from app.core.exceptions import BizException
+from app.schemas.saved_screen import PublicScreen
+from app.services.screens import public_page
+
+router = APIRouter(prefix="/public", tags=["Public"])
+
+
+@router.get("/screens/{share_id}")
+async def get_public_screen(
+    share_id: str, service: Service
+) -> ApiResponse[PublicScreen]:
+    """线上版本：返回发布快照，不是草稿；已下线、已删除、不存在都是 404"""
+    summary, snapshot = await service.get_live(share_id)
+    return success_response(
+        PublicScreen(
+            name=summary.name,
+            page=public_page(snapshot.page),
+            version=snapshot.version,
+            published_at=snapshot.published_at,
+        )
+    )
+
+
+@router.get("/screens/{share_id}/datasources/{datasource_id}")
+async def fetch_public_datasource(
+    share_id: str, datasource_id: str, service: Service
+) -> ApiResponse[dict[str, Any] | list[Any]]:
+    """线上取数：地址取自已发布快照里的数据源配置，前端只传 ID"""
+    return success_response(
+        await service.fetch_live_datasource(share_id, datasource_id)
+    )
+
+
+@router.get("/thumbnails/{thumbnail_id}")
+async def get_thumbnail(thumbnail_id: str, service: Service) -> FileResponse:
+    opened = service.open_thumbnail(thumbnail_id)
+    if opened is None:
+        raise BizException(404, "封面不存在")
+    path, media_type = opened
+    # 每次上传都换新 ID，内容永远不变，可以放心长期缓存
+    return FileResponse(
+        path,
+        media_type=media_type,
+        headers={"Cache-Control": "public, max-age=31536000, immutable"},
+    )