feat: deutsche Betragsanzeige (eur-Filter) und deutsche GUI-Labels

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

finance/app/routers/gui.py

@@ -10,6 +10,7 @@ from app.auth import COOKIE, session_valid
 from app.db import get_session
 from app.engine.loans import add_months
 from app.engine.recurrence import occurrences
+from app.formats import de_label, eur
 from app.models.tables import (Account, Category, PlannedItem,
                                ProjectionResult, RecurringItem,
                                ScenarioLoan, ScenarioModifier, Transaction)
@@ -28,6 +29,8 @@ PAGE_SIZE = 50
 
 templates = Jinja2Templates(directory="app/templates")
 templates.env.globals["app_version"] = get_version()
+templates.env.filters["eur"] = eur
+templates.env.filters["de_label"] = de_label
 router = APIRouter()