feat: window management system with minimize, fullscreen, and AI chat split

- Window manager store (Zustand) for managing open/minimized/fullscreen windows
- Window component with header controls: KI-Chat toggle, fullscreen, minimize, close
- AI chat panel with streaming chat via existing /ai/sessions API
- WindowContainer renders all non-minimized windows
- TopBar shows minimized windows as clickable pills
- ContactEditForm extracted from ContactEditModal for window rendering
- ContactsList and ContactDetailPage use openWindow() instead of modal state
- Draggable windows with z-index management

frontend/src/pages/ContactDetailPage.tsx

@@ -6,7 +6,8 @@ import React from 'react';
 import { useParams, useNavigate } from 'react-router-dom';
 import { useTranslation } from 'react-i18next';
 import { ContactDetail } from '@/components/contacts/ContactDetail';
-import { ContactEditModal } from '@/components/contacts/ContactEditModal';
+import { ContactEditForm } from '@/components/contacts/ContactEditForm';
+import { useWindowStore } from '@/store/windowStore';
 import { useUnifiedContact, type UnifiedContact } from '@/api/hooks';
 import { Button } from '@/components/ui/Button';
 import { ChevronLeft } from 'lucide-react';
@@ -16,13 +17,20 @@ export function ContactDetailPage() {
   const { id } = useParams<{ id: string }>();
   const navigate = useNavigate();
   const { data: contact, isLoading } = useUnifiedContact(id);
-  const [editModalOpen, setEditModalOpen] = React.useState(false);
-  const [editingContact, setEditingContact] = React.useState<UnifiedContact | null>(null);
+  const openWindow = useWindowStore((s) => s.openWindow);
 
   const handleEdit = () => {
     if (contact) {
-      setEditingContact(contact);
-      setEditModalOpen(true);
+      openWindow({
+        title: t('contacts.edit'),
+        type: 'contact-edit',
+        component: ContactEditForm,
+        componentProps: {
+          contact,
+          onClose: () => {},
+          onSaved: () => {},
+        },
+      });
     }
   };
 
@@ -30,11 +38,6 @@ export function ContactDetailPage() {
     navigate('/contacts');
   };
 
-  const handleSaved = () => {
-    setEditModalOpen(false);
-    setEditingContact(null);
-  };
-
   return (
     <div className="flex flex-col h-full" data-testid="contact-detail-page">
       <div className="flex items-center gap-2 px-4 py-2 border-b border-secondary-200 bg-white">
@@ -55,12 +58,6 @@ export function ContactDetailPage() {
           onDeleted={handleDeleted}
         />
       </div>
-      <ContactEditModal
-        open={editModalOpen}
-        onClose={() => setEditModalOpen(false)}
-        contact={editingContact}
-        onSaved={handleSaved}
-      />
     </div>
   );
 }