feat: Start/Ende fuer Fixposten in der GUI + Datumsvalidierung

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

finance/app/routers/planning.py

@@ -3,7 +3,7 @@ from decimal import Decimal
 from typing import Literal
 
 from fastapi import APIRouter, Depends, HTTPException
-from pydantic import BaseModel, ConfigDict, Field
+from pydantic import BaseModel, ConfigDict, Field, model_validator
 from sqlalchemy import delete, select
 from sqlalchemy.orm import Session
 
@@ -28,6 +28,13 @@ class RecurringIn(BaseModel):
     end_date: date | None = None
     category_id: int | None = None
 
+    @model_validator(mode="after")
+    def _ende_nicht_vor_start(self):
+        if (self.start_date is not None and self.end_date is not None
+                and self.end_date < self.start_date):
+            raise ValueError("Ende darf nicht vor Start liegen")
+        return self
+
 
 class RecurringOut(RecurringIn):
     model_config = ConfigDict(from_attributes=True)
@@ -90,6 +97,10 @@ def patch_recurring(item_id: int, data: RecurringPatch,
         _check_category(session, fields["category_id"])
     for key, value in fields.items():
         setattr(item, key, value)
+    if (item.start_date is not None and item.end_date is not None
+            and item.end_date < item.start_date):
+        session.rollback()
+        raise HTTPException(422, "Ende darf nicht vor Start liegen")
     session.commit()
     session.refresh(item)
     return RecurringOut.model_validate(item)