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/crypto.py

@@ -0,0 +1,42 @@
+from __future__ import annotations
+
+import json
+from typing import Any
+
+from cryptography.fernet import Fernet, InvalidToken
+
+
+class SecretVault:
+    def __init__(self, key: str) -> None:
+        try:
+            self._fernet = Fernet(key.encode("ascii"))
+        except (ValueError, TypeError) as exc:
+            raise ValueError("DATAHUB_ENCRYPTION_KEY 格式无效。") from exc
+
+    @staticmethod
+    def generate_key() -> str:
+        return Fernet.generate_key().decode("ascii")
+
+    def encrypt_json(self, payload: dict[str, Any]) -> str:
+        raw = json.dumps(payload, ensure_ascii=False, separators=(",", ":")).encode("utf-8")
+        return self._fernet.encrypt(raw).decode("ascii")
+
+    def decrypt_json(self, token: str) -> dict[str, Any]:
+        if not token:
+            return {}
+        try:
+            payload = json.loads(self._fernet.decrypt(token.encode("ascii")).decode("utf-8"))
+        except (InvalidToken, UnicodeDecodeError, json.JSONDecodeError) as exc:
+            raise ValueError("凭据无法解密，请检查 DATAHUB_ENCRYPTION_KEY。") from exc
+        if not isinstance(payload, dict):
+            raise ValueError("凭据格式无效。")
+        return payload
+
+
+def mask_secret(value: str, last_n: int = 4) -> str:
+    text = str(value or "")
+    if not text:
+        return ""
+    if len(text) <= last_n:
+        return "*" * len(text)
+    return ("*" * max(4, len(text) - last_n)) + text[-last_n:]