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/components/ui/DecimalInput.jsx

@@ -0,0 +1,36 @@
+/**
+ * ==========================================================
+ * OMSORG BUSINESS CONTROLS PRO
+ * Component: DecimalInput
+ * Sprint: 0.2.0
+ * ==========================================================
+ */
+
+import { sanitizeDecimalInput } from "../../utils/germanDecimal";
+
+export default function DecimalInput({
+  value,
+  onChange,
+  placeholder,
+  required = false,
+  disabled = false,
+  id,
+}) {
+  function handleChange(event) {
+    onChange(sanitizeDecimalInput(event.target.value));
+  }
+
+  return (
+    <input
+      type="text"
+      inputMode="decimal"
+      pattern="[0-9]*[.,]?[0-9]*"
+      value={value}
+      onChange={handleChange}
+      placeholder={placeholder}
+      required={required}
+      disabled={disabled}
+      id={id}
+    />
+  );
+}