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/ratelimit.py

@@ -0,0 +1,36 @@
+from __future__ import annotations
+
+import threading
+import time
+
+
+class TokenBucket:
+    def __init__(self, rate_per_minute: float, capacity: float | None = None, clock=time.monotonic) -> None:
+        self.rate_per_second = max(0.001, rate_per_minute / 60.0)
+        self.capacity = float(capacity if capacity is not None else rate_per_minute)
+        self._tokens = self.capacity
+        self._updated = clock()
+        self._clock = clock
+        self._lock = threading.Lock()
+
+    def acquire(self, tokens: float = 1.0, block: bool = True) -> bool:
+        while True:
+            with self._lock:
+                now = self._clock()
+                elapsed = max(0.0, now - self._updated)
+                self._tokens = min(self.capacity, self._tokens + elapsed * self.rate_per_second)
+                self._updated = now
+                if self._tokens >= tokens:
+                    self._tokens -= tokens
+                    return True
+                wait = (tokens - self._tokens) / self.rate_per_second
+            if not block:
+                return False
+            time.sleep(min(wait, 0.05))
+
+    @property
+    def remaining(self) -> float:
+        with self._lock:
+            now = self._clock()
+            elapsed = max(0.0, now - self._updated)
+            return min(self.capacity, self._tokens + elapsed * self.rate_per_second)