feat: Kunden archivieren + Ticket-Status-Checkbox-Filter

Kunden:
- Neues Feld customers.archived; Archivieren/Wiederherstellen-Button in der
  Kundendetailseite, 'Archiviert'-Badge
- CustomersPage: vierter Filter-Tab 'Archiviert'; archivierte Kunden aus
  Alle/Leads/Feste Kunden ausgeblendet, nur im Archiv-Tab sichtbar

Tickets:
- Status-Mehrfachauswahl per Checkbox im Filterbereich; Default alle Status
  ausser 'Closed' (= archiviert). 'Standard' / 'Alle inkl. Archiv' Shortcuts
- useWorkorders: Statusfilter serverseitig via Query.equal(array) statt
  Client-Filter nach dem Limit (behebt Bug, bei dem archivierte Tickets die
  neuesten Slots belegten und aktive verdraengten)

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

src/pages/CustomersPage.jsx

@@ -3,19 +3,23 @@ import { Link } from 'react-router-dom'
 import { FaSpinner, FaPlus, FaStar, FaFileInvoiceDollar, FaFileLines } from 'react-icons/fa6'
 import { useCustomers } from '../hooks/useCustomers'
 import { useAuth } from '../context/AuthContext'
-import { createLead, customerStage } from '../lib/leads'
+import { createLead, customerStage, isArchived } from '../lib/leads'
 import { PageHeader, Card, Button, Badge, EmptyState, Field } from '../components/ui'
 
 export default function CustomersPage() {
   const { customers, loading, refresh } = useCustomers()
   const { user } = useAuth()
   const [search, setSearch] = useState('')
-  const [stage, setStage] = useState('all') // all | lead | customer
+  const [stage, setStage] = useState('all') // all | lead | customer | archived
   const [showCreate, setShowCreate] = useState(false)
 
   const filtered = useMemo(() => {
     return (customers || [])
       .filter((c) => {
+        const archived = isArchived(c)
+        // Archivierte nur im Archiviert-Tab, sonst nie
+        if (stage === 'archived') return archived
+        if (archived) return false
         const st = customerStage(c)
         if (st === 'lost') return stage === 'all'
         if (stage === 'all') return true
@@ -56,6 +60,7 @@ export default function CustomersPage() {
             <button className={stage === 'all' ? 'active' : ''} onClick={() => setStage('all')}>Alle</button>
             <button className={stage === 'lead' ? 'active' : ''} onClick={() => setStage('lead')}>Leads</button>
             <button className={stage === 'customer' ? 'active' : ''} onClick={() => setStage('customer')}>Feste Kunden</button>
+            <button className={stage === 'archived' ? 'active' : ''} onClick={() => setStage('archived')}>Archiviert</button>
           </div>
           <input className="form-control search-input" placeholder="Kunde suchen..." value={search} onChange={(e) => setSearch(e.target.value)} style={{ maxWidth: 320 }} />
         </div>
@@ -77,11 +82,12 @@ export default function CustomersPage() {
                       <div style={{ fontWeight: 700, display: 'flex', alignItems: 'center', gap: 8 }}>
                         {c.importantCustomer && <FaStar style={{ color: 'var(--warn)' }} title="Wichtiger Kunde" />}
                         {c.name}
-                        {c.code && <span className="faint" style={{ fontWeight: 400 }}>· {c.code}</span>}
+                        {c.code && <span className="faint" style={{ fontWeight: 400 }}>� {c.code}</span>}
                       </div>
-                      <div className="muted">{[c.location, c.email].filter(Boolean).join(' · ') || '-'}</div>
+                      <div className="muted">{[c.location, c.email].filter(Boolean).join(' � ') || '-'}</div>
                     </div>
                     <div className="flex gap-2 wrap" style={{ justifyContent: 'flex-end' }}>
+                      {isArchived(c) && <Badge tone="muted">Archiviert</Badge>}
                       {st === 'lead' && <Badge tone="warn" dot>Lead</Badge>}
                       {st === 'customer' && <Badge tone="ok" dot>Fester Kunde</Badge>}
                       {st === 'lost' && <Badge tone="muted">Abgesagt</Badge>}