Add birthday reminder widget to omsorgapp dashboard (FR-MA-7)

Also fixes date-input fields on the employee form (dateOfBirth/entryDate/
exitDate) to convert the generated client's Date objects into the
"YYYY-MM-DD" string <input type="date"> expects — needed for the widget's
birthday calculation and previously left the fields blank on edit.

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

omsorgapp/src/modules/home/HomePage.jsx

@@ -5,6 +5,7 @@ import HomeStats from "./HomeStats";
 import OmsorgBadge from "../../components/ui/OmsorgBadge";
 import FollowUpWidget from "./FollowUpWidget";
 import OrderStatusWidget from "./OrderStatusWidget";
+import BirthdayWidget from "./BirthdayWidget";
 export default function HomePage() {
   return (
     <>
@@ -31,6 +32,7 @@ export default function HomePage() {
       <section className="dashboard-grid home-grid">
         <FollowUpWidget />
         <OrderStatusWidget />
+        <BirthdayWidget />
 
         <OmsorgCard title="Schnellaktionen">
           <div className="home-actions">