Replace seenByTenant boolean with seenByTenantAt timestamp field

Update location tracking to record when tenant views a location rather than just whether they've seen it. This provides better audit trail and enables future features like viewing history.

Changes:
- Convert seenByTenant (boolean) to seenByTenantAt (Date) in database schema
- Update setSeenByTenantAt action to store timestamp instead of boolean flag
- Modify LocationCard UI to display when location was seen by tenant
- Update all references across locationActions, monthActions, and view components
- Remove unused imports from ViewLocationCard

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

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

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

@@ -1,5 +1,5 @@
 import { ViewLocationCard } from '@/app/ui/ViewLocationCard';
-import { fetchLocationById, setSeenByTenant } from '@/app/lib/actions/locationActions';
+import { fetchLocationById, setSeenByTenantAt } from '@/app/lib/actions/locationActions';
 import { getUserSettingsByUserId } from '@/app/lib/actions/userSettingsActions';
 import { notFound } from 'next/navigation';
 import { myAuth } from '@/app/lib/auth';
@@ -20,7 +20,7 @@ export default async function LocationViewPage({ locationId }: { locationId:stri
 
     // If the page is not visited by the owner, mark it as seen by tenant
     if (!isOwner) {
-        await setSeenByTenant(locationId);
+         await setSeenByTenantAt(locationId);
     }
 
     return (<ViewLocationCard location={location} userSettings={userSettings} />);