feat(HEL-382): 搭建 datahub 底座和盘后正式数据链路

新增独立 xiaobai-datahub 服务（SQLite WAL、Tushare 盘后发布、/v1 契约和管理后台），不改现站页面与数据链路。

Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: multica-agent <github@multica.ai>

xiaobai-datahub/datahub/governance/retry.py

@@ -0,0 +1,35 @@
+from __future__ import annotations
+
+import time
+from collections.abc import Callable
+from typing import TypeVar
+
+T = TypeVar("T")
+
+
+class RetryError(RuntimeError):
+    def __init__(self, message: str, attempts: int, last_error: BaseException | None = None) -> None:
+        super().__init__(message)
+        self.attempts = attempts
+        self.last_error = last_error
+
+
+def retry_call(
+    fn: Callable[[], T],
+    attempts: int = 5,
+    base_delay: float = 0.2,
+    max_delay: float = 8.0,
+    sleeper: Callable[[float], None] = time.sleep,
+    retry_on: tuple[type[BaseException], ...] = (Exception,),
+) -> T:
+    last: BaseException | None = None
+    for attempt in range(1, max(1, attempts) + 1):
+        try:
+            return fn()
+        except retry_on as exc:
+            last = exc
+            if attempt >= attempts:
+                break
+            delay = min(max_delay, base_delay * (2 ** (attempt - 1)))
+            sleeper(delay)
+    raise RetryError(f"retry exhausted after {attempts} attempts: {last}", attempts, last)