auto-assign filter priority (max+10) on create

New filter rules no longer default to priority 100. Server picks
max(priority)+10 per account when client sends priority=None (or 10
if the account has no rules yet), and the UI pre-fills the input
with the next value instead of a fixed 100. Avoids ambiguous ordering
when multiple rules end up with the same priority.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/routers/filters.py

@@ -1,4 +1,5 @@
 from fastapi import APIRouter, Depends, HTTPException
+from sqlalchemy import func
 from sqlalchemy.orm import Session
 
 import logging
@@ -52,10 +53,20 @@ def create_filter(data: FilterRuleCreate, db: Session = Depends(get_db)):
     if not account:
         raise HTTPException(404, "Konto nicht gefunden")
 
+    if data.priority is None:
+        # Ans Ende einsortieren: max(priority) + 10 für dieses Konto. Falls noch
+        # keine Regel existiert, starten wir bei 10.
+        current_max = db.query(func.max(FilterRule.priority)).filter(
+            FilterRule.account_id == data.account_id
+        ).scalar()
+        priority = (current_max + 10) if current_max is not None else 10
+    else:
+        priority = data.priority
+
     rule = FilterRule(
         account_id=data.account_id,
         name=data.name,
-        priority=data.priority,
+        priority=priority,
         enabled=data.enabled,
         stop_processing=data.stop_processing,
         source_folder=data.source_folder,