feat(tasks): Benutzer-Suche beim Teilen (statt Freitext)

Analog zu Kontakten/Kalender: ab 2 Zeichen werden Vorschlaege per
/users/search eingeblendet.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/views/TasksView.vue

@@ -113,7 +113,16 @@
         <div v-if="menuList.permission === 'owner'" class="field">
           <label>Mit Benutzer teilen</label>
           <div class="share-row">
-            <InputText v-model="shareUsername" placeholder="Benutzername" fluid />
+            <div style="position: relative; flex: 1;">
+              <InputText v-model="shareUsername" placeholder="Benutzername suchen..."
+                         fluid @input="onShareSearch" />
+              <div v-if="shareSearchResults.length" class="user-search-popup">
+                <div v-for="u in shareSearchResults" :key="u.id" class="user-result"
+                     @click="shareUsername = u.username; shareSearchResults = []">
+                  <i class="pi pi-user"></i> {{ u.username }}
+                </div>
+              </div>
+            </div>
             <Select v-model="sharePermission" :options="permOptions" optionLabel="label" optionValue="value" />
             <Button label="Teilen" size="small" @click="doShare" />
           </div>
@@ -238,6 +247,20 @@ const menuList = ref(null)
 const shareUsername = ref('')
 const sharePermission = ref('read')
 const listShares = ref([])
+const shareSearchResults = ref([])
+let shareSearchTimer = null
+
+function onShareSearch() {
+  clearTimeout(shareSearchTimer)
+  const q = shareUsername.value.trim()
+  if (q.length < 2) { shareSearchResults.value = []; return }
+  shareSearchTimer = setTimeout(async () => {
+    try {
+      const res = await apiClient.get('/users/search', { params: { q } })
+      shareSearchResults.value = res.data
+    } catch { shareSearchResults.value = [] }
+  }, 250)
+}
 const permOptions = [
   { label: 'Lesen', value: 'read' },
   { label: 'Lesen+Schreiben', value: 'readwrite' },
@@ -353,6 +376,7 @@ async function createList() {
 function openListMenu(tl) {
   menuList.value = tl
   shareUsername.value = ''
+  shareSearchResults.value = []
   showListMenu.value = true
   loadShares()
 }
@@ -373,6 +397,7 @@ async function doShare() {
     })
     toast.add({ severity: 'success', summary: 'Geteilt', life: 2500 })
     shareUsername.value = ''
+    shareSearchResults.value = []
     await loadShares()
   } catch (err) {
     toast.add({ severity: 'error', summary: err.response?.data?.error || 'Fehler', life: 4000 })
@@ -621,7 +646,14 @@ watch(selectedListId, loadTasks)
 .field label { display: block; margin-bottom: 0.25rem; font-weight: 500; font-size: 0.875rem; }
 .field-row { display: flex; gap: 0.75rem; }
 .field-row .field { flex: 1; }
-.share-row { display: flex; gap: 0.5rem; align-items: center; }
+.share-row { display: flex; gap: 0.5rem; align-items: center; flex-wrap: wrap; }
+.user-search-popup { position: absolute; top: 100%; left: 0; right: 0; z-index: 10;
+                     background: white; border: 1px solid var(--p-surface-200);
+                     border-radius: 4px; max-height: 160px; overflow-y: auto;
+                     box-shadow: 0 4px 12px rgba(0,0,0,0.1); }
+.user-result { padding: 0.5rem 0.75rem; cursor: pointer; font-size: 0.875rem;
+               display: flex; gap: 0.5rem; align-items: center; }
+.user-result:hover { background: var(--p-primary-50); }
 .existing-shares { margin-top: 0.5rem; }
 .share-perm-item { display: flex; align-items: center; gap: 0.5rem; padding: 0.375rem 0; font-size: 0.875rem; }
 .perm-label { color: var(--p-text-muted-color); font-size: 0.75rem; }