feat: gleiches Schlagwort für Einnahme UND Ausgabe erlaubt (Art je Regel)

- CategorizationRule bekommt `kind` (expense|income|transfer); Unique jetzt
  (owner, match_field, pattern, kind) statt ohne kind
- Konfliktprüfung/Anlage (add/update Keyword, Transfer-Keyword, gelernte Regeln)
  arbeiten kind-bewusst: dasselbe Wort je einmal pro Art möglich
- Migration 0009 mit Backfill (kind aus Kategorie-Art bzw. is_transfer)
- Tests angepasst: quer über Arten erlaubt, gleiche Art weiterhin Konflikt (71 grün)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/app/routers/categories.py

@@ -220,11 +220,14 @@ def _conflict(db: Session, clash: CategorizationRule) -> HTTPException:
     )
 
 
-def _find_any_rule(db: Session, user: User, pattern: str, exclude_id: int | None = None):
+def _find_any_rule(db: Session, user: User, pattern: str, kind: str, exclude_id: int | None = None):
+    """Sucht ein manuelles Schlagwort gleicher Art (kind). Dasselbe Wort darf je
+    einmal für Ausgabe, Einnahme und Transfer existieren – Konflikt nur je Art."""
     q = db.query(CategorizationRule).filter(
         CategorizationRule.owner_id == user.id,
         CategorizationRule.match_field == MatchField.any,
         CategorizationRule.pattern == pattern,
+        CategorizationRule.kind == kind,
     )
     if exclude_id is not None:
         q = q.filter(CategorizationRule.id != exclude_id)
@@ -279,7 +282,7 @@ def update_keyword(
     if not pattern:
         raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail="Leeres Schlagwort")
     if pattern != rule.pattern:
-        clash = _find_any_rule(db, user, pattern, exclude_id=rule.id)
+        clash = _find_any_rule(db, user, pattern, rule.kind, exclude_id=rule.id)
         if clash is not None:
             raise _conflict(db, clash)
         rule.pattern = pattern
@@ -329,14 +332,15 @@ def add_keyword(
     pattern = normalize_text(payload.word)[:255]
     if not pattern:
         raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail="Leeres Schlagwort")
-    existing = _find_any_rule(db, user, pattern)
+    kind = cat.type.value  # "expense" | "income" – Konflikt nur innerhalb derselben Art
+    existing = _find_any_rule(db, user, pattern, kind)
     if existing is not None:
         if not existing.is_transfer and existing.category_id == cat.id and existing.amount_cents == payload.amount_cents:
             return _keyword_out(existing)  # schon identisch vorhanden – unverändert zurück
         raise _conflict(db, existing)
     rule = CategorizationRule(
         owner_id=user.id, match_field=MatchField.any, pattern=pattern,
-        category_id=cat.id, amount_cents=payload.amount_cents,
+        category_id=cat.id, amount_cents=payload.amount_cents, kind=kind,
         source=RuleSource.manual, priority=10,
     )
     db.add(rule)
@@ -374,7 +378,7 @@ def add_transfer_keyword(
     pattern = normalize_text(payload.word)[:255]
     if not pattern:
         raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail="Leeres Schlagwort")
-    existing = _find_any_rule(db, user, pattern)
+    existing = _find_any_rule(db, user, pattern, "transfer")
     if existing is not None:
         if existing.is_transfer and existing.amount_cents == payload.amount_cents:
             return _transfer_keyword_out(existing)
@@ -382,7 +386,7 @@ def add_transfer_keyword(
     rule = CategorizationRule(
         owner_id=user.id, match_field=MatchField.any, pattern=pattern,
         category_id=None, amount_cents=payload.amount_cents, is_transfer=True,
-        source=RuleSource.manual, priority=10,
+        kind="transfer", source=RuleSource.manual, priority=10,
     )
     db.add(rule)
     db.commit()