Add German comma decimal input for currency/decimal fields

- New utility module `germanDecimal.js` with parseGermanDecimal(),
  sanitizeDecimalInput(), and formatGermanDecimal()
- New DecimalInput component replacing type="number" inputs
- Enables users to enter comma as decimal separator (12,50)
- Applied to: hourlyWage, weeklyHours (ContractForm)
  and billingRate, travelCostRate, travelCostPerKm,
  mealAllowanceRate, minimumHours, and percent surcharges (FacilityForm)
- Display formatting updated in FacilityDetailPanel to show comma decimals

Both comma and dot are accepted as decimal separators. Backend
decimal types remain unchanged (already decimal?).

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

omsorgapp/src/modules/employees/ContractForm.jsx

@@ -1,5 +1,7 @@
 import OmsorgButton from "../../components/ui/OmsorgButton";
+import DecimalInput from "../../components/ui/DecimalInput";
 import { useValueListItems } from "../../app/useValueListItems";
+import { parseGermanDecimal } from "../../utils/germanDecimal";
 
 export const emptyContractForm = {
   contractType: "",
@@ -36,8 +38,8 @@ export function contractFormToPayload(form, { employeeId, includeStatus = false
     facilityId: null,
     startDate: form.startDate,
     endDate: form.endDate || null,
-    weeklyHours: form.weeklyHours === "" ? null : Number(form.weeklyHours),
-    hourlyWage: form.hourlyWage === "" ? null : Number(form.hourlyWage),
+    weeklyHours: parseGermanDecimal(form.weeklyHours),
+    hourlyWage: parseGermanDecimal(form.hourlyWage),
     allowancesDescription: form.allowancesDescription.trim() || null,
     overtimeRules: form.overtimeRules.trim() || null,
     vacationDaysPerYear: form.vacationDaysPerYear === "" ? null : Number(form.vacationDaysPerYear),
@@ -59,6 +61,10 @@ export default function ContractForm({ form, onChange, includeStatus = false })
     return (event) => onChange({ ...form, [field]: event.target.value });
   }
 
+  function updateDecimalField(field) {
+    return (rawValue) => onChange({ ...form, [field]: rawValue });
+  }
+
   return (
     <div className="form-grid">
       <label className="form-field">
@@ -101,12 +107,12 @@ export default function ContractForm({ form, onChange, includeStatus = false })
       <div className="form-row">
         <label className="form-field">
           <span>Arbeitszeit (Std./Woche)</span>
-          <input type="number" min="0" step="0.5" value={form.weeklyHours} onChange={updateField("weeklyHours")} />
+          <DecimalInput value={form.weeklyHours} onChange={updateDecimalField("weeklyHours")} />
         </label>
 
         <label className="form-field">
           <span>Stundenlohn (€)</span>
-          <input type="number" min="0" step="0.01" value={form.hourlyWage} onChange={updateField("hourlyWage")} />
+          <DecimalInput value={form.hourlyWage} onChange={updateDecimalField("hourlyWage")} />
         </label>
       </div>