feat(ui): one CountBadge for all counters; counters on tab corners

- CountBadge component (accent / muted, inline / corner, 99+, showZero);
  used in the nav bar, task list and list tabs, admin organizations and
  numeric badges of the mobile menu; old badge-count removed
- Counters sit on the top right corner of tabs; "Alle Aufgaben" gets one
  (desktop tab and mobile menu)
- Open/done task counters include tasks in shared lists, matching what
  "Alle Aufgaben" shows (nav counter was too low)
- Theme template derives --accent-dim/--accent-border from the accent
- Docs: ui-patterns counters section

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/features/lists/SharedListsView.tsx

@@ -14,6 +14,7 @@ import { ListItem, SharedList, ListShare, Team, User, WSMessage } from '../../li
 import { api, buildWebSocketURL, triggerHaptic, createRealtimeConnection, RealtimeTransport } from '../../lib/api';
 import { UnifiedShareModal } from '../../components/UnifiedShareModal';
 import { AvatarStack, AvatarPerson } from '../../components/AvatarStack';
+import { CountBadge } from '../../components/CountBadge';
 import { useMobileActions } from '../../context/MobileActionContext';
 
 interface SharedListsViewProps {
@@ -842,8 +843,8 @@ export const SharedListsView: React.FC<SharedListsViewProps> = ({ onRefreshGloba
     <div className="w-full space-y-3">
       {/* Top Header: List Tabs & Actions (Desktop) */}
       <div className="hidden sm:flex flex-wrap items-center justify-between gap-2 border-b border-border pb-2 !mt-0">
-        {/* List Tabs */}
-        <div className="flex flex-wrap items-center gap-1">
+        {/* List Tabs (counters sit on the top right corner, hence the extra gap) */}
+        <div className="flex flex-wrap items-center gap-x-3 gap-y-3 pt-2">
           {lists.map((lst) => {
             const openCount = deduplicateItems(lst.items || []).filter((i) => !i.isCompleted).length;
             const isSelected = activeList?.id === lst.id;
@@ -860,9 +861,6 @@ export const SharedListsView: React.FC<SharedListsViewProps> = ({ onRefreshGloba
                 >
                   <span>{lst.icon}</span>
                   <span>{lst.title}</span>
-                  {openCount > 0 && (
-                    <span className="ml-1 badge-count">{openCount}</span>
-                  )}
                   <AvatarStack
                     people={otherMembers(lst)}
                     size="xxs"
@@ -870,6 +868,7 @@ export const SharedListsView: React.FC<SharedListsViewProps> = ({ onRefreshGloba
                     className="ml-0.5"
                   />
                 </button>
+                <CountBadge count={openCount} position="corner" />
                 {isSelected && lists.length > 1 && (
                   <button
                     onClick={() => handleDeleteList(lst.id)}