feat(sidebar): tooltip for the active-session indicator dot (#782)

The pulsing green dot next to a session row signals that the session
had activity in the last 10 minutes, but the meaning was undocumented.
Hovering it now shows a translated tooltip, and an aria-label exposes
the same text to screen readers.

Uses the existing shared Tooltip component (portal-positioned, so it
is not clipped by the sidebar overflow). Translation key added to all
eight sidebar locale files (en, de, it, ja, ko, ru, tr, zh-CN).

src/components/sidebar/view/subcomponents/SidebarSessionItem.tsx

@@ -1,7 +1,7 @@
 import { Check, Edit2, Trash2, X } from 'lucide-react';
 import type { TFunction } from 'i18next';
 
-import { Badge, Button } from '../../../../shared/view/ui';
+import { Badge, Button, Tooltip } from '../../../../shared/view/ui';
 import { cn } from '../../../../lib/utils';
 import type { Project, ProjectSession, LLMProvider } from '../../../../types/app';
 import type { SessionWithProvider } from '../../types/types';
@@ -97,7 +97,13 @@ export default function SidebarSessionItem({
     <div className="group relative">
       {sessionView.isActive && (
         <div className="absolute left-0 top-1/2 -translate-x-1 -translate-y-1/2 transform">
-          <div className="h-2 w-2 animate-pulse rounded-full bg-green-500" />
+          <Tooltip content={t('tooltips.activeSessionIndicator')} position="right">
+            <div
+              role="status"
+              aria-label={t('tooltips.activeSessionIndicator')}
+              className="h-2 w-2 animate-pulse rounded-full bg-green-500"
+            />
+          </Tooltip>
         </div>
       )}