Add seenByTenant tracking feature

- Add seenByTenant field to BillingLocation interface
- Implement setSeenByTenant function to mark locations as viewed by tenant
  - Checks if flag is already set to avoid unnecessary DB updates
  - Includes TypeDoc documentation
- Update LocationViewPage to call setSeenByTenant when non-owner visits
- Add seenByTenant to fetchAllLocations projection
- Update LocationCard to show "seen by tenant" status indicator
  - Displays in "Monthly statement" fieldset with checkmark icon
  - Shows alongside monthly expense total
- Add localization strings for monthly statement and seen status

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/[locale]/share/location/[id]/LocationViewPage.tsx

@@ -1,6 +1,7 @@
 import { ViewLocationCard } from '@/app/ui/ViewLocationCard';
-import { fetchLocationById } from '@/app/lib/actions/locationActions';
+import { fetchLocationById, setSeenByTenant } from '@/app/lib/actions/locationActions';
 import { notFound } from 'next/navigation';
+import { myAuth } from '@/app/lib/auth';
 
 export default async function LocationViewPage({ locationId }: { locationId:string }) {
     const location = await fetchLocationById(locationId);
@@ -9,5 +10,14 @@ export default async function LocationViewPage({ locationId }: { locationId:stri
         return(notFound());
     }
 
+    // Check if the page was accessed by an authenticated user who is the owner
+    const session = await myAuth();
+    const isOwner = session?.user?.id === location.userId;
+  
+    // If the page is not visited by the owner, mark it as seen by tenant
+    if (!isOwner) {
+        await setSeenByTenant(locationId);
+    }
+
     return (<ViewLocationCard location={location} />);
 }