refactor(server): split oversized backend services

server/src/app/services/expense_claim_errors.py

@@ -0,0 +1,7 @@
+from __future__ import annotations
+
+
+class ExpenseClaimSubmissionBlockedError(ValueError):
+    def __init__(self, issues: list[str]) -> None:
+        self.issues = [str(issue or "").strip() for issue in issues if str(issue or "").strip()]
+        super().__init__("提交前请先补全信息：" + "；".join(self.issues))