fix: tolerante GUI-Filter, sichtbare Bedienelemente, fixierte Navigation

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

finance/app/routers/gui.py

@@ -62,6 +62,28 @@ def _latest_projection(session: Session) -> ProjectionResult | None:
     ).scalars().first()
 
 
+def _opt_int(value: str | None) -> int | None:
+    """Wandelt einen GUI-Query-Parameter tolerant in int|None um. HTML-Formulare
+    senden bei nicht ausgefüllten Feldern leere Strings statt gar keinen
+    Parameter - das darf nie zu einem 422 fuehren, sondern degradiert zu None."""
+    if value is None or not value.strip():
+        return None
+    try:
+        return int(value)
+    except ValueError:
+        return None
+
+
+def _opt_date(value: str | None) -> date | None:
+    """Wie _opt_int, nur fuer date-Felder (ISO-Format aus <input type=date>)."""
+    if value is None or not value.strip():
+        return None
+    try:
+        return date.fromisoformat(value)
+    except ValueError:
+        return None
+
+
 @router.get("/", dependencies=[Depends(gui_session)])
 def index(request: Request, session: Session = Depends(get_session)):
     accounts = session.execute(select(Account)).scalars().all()
@@ -77,15 +99,23 @@ def index(request: Request, session: Session = Depends(get_session)):
 @router.get("/buchungen", dependencies=[Depends(gui_session)])
 def buchungen(
     request: Request,
-    account_id: int | None = None,
-    date_from: date | None = None,
-    date_to: date | None = None,
-    category_id: int | None = None,
+    account_id: str | None = None,
+    date_from: str | None = None,
+    date_to: str | None = None,
+    category_id: str | None = None,
     q: str | None = None,
     status: str = "confirmed",
     page: int = 1,
     session: Session = Depends(get_session),
 ):
+    # HTML-Filterformular sendet leere Strings fuer nicht ausgefuellte Felder -
+    # daher hier bewusst str|None statt int|None/date|None und tolerante
+    # Konvertierung, statt FastAPI vor dem Handler mit 422 abbrechen zu lassen.
+    # Die API-Routen (/api/transactions) bleiben strikt typisiert.
+    account_id = _opt_int(account_id)
+    date_from = _opt_date(date_from)
+    date_to = _opt_date(date_to)
+    category_id = _opt_int(category_id)
     page = max(1, page)
     total = count_transactions(
         account_id=account_id,