Search monitors across all pages

[tomschlick]

Summary

• Apply monitors list search at the table level so it queries the full dataset before pagination
• Cover name, target, description, and tags, with a clearer “Search all monitors” placeholder
• Add a regression test that finds monitors on other pages (and from page 2 back to page 1)

Test plan

• Open /admin/monitors with enough monitors to paginate
• Search for a monitor that only appears on page 2+ and confirm it shows up
• Search by target, description, and tag as well as name
• Confirm tests/Feature/Filament/MonitorResourceTest.php passes