refactor(housekeeping): split client, add loading states, URL persistence, fix dead code

- Split ManageClient into ManageSection, PresetsSection, TestSection,
  ImportSection, ExportSection - each tab only renders what it needs
- Add loading/disabled states to preset, import, export, clear buttons
- Persist search and group filter via URL searchParams (survives refresh)
- Remove dead getAuditHistory export from actions
- Fix testRankPermission - remove unnecessary revalidatePath with JSON result
- Clean up unused errors/count variables in bulkImportPermissions
- Add 'loading' translation key to housekeeping section (en/nl)

src/messages/nl.json

@@ -1881,6 +1881,7 @@
 				"invalidRank": "Ongeldige rang",
 				"testDone": "Test voltooid: {count} permissies gevonden",
 				"testing": "Testen...",
+				"loading": "Laden...",
 				"prev": "Vorige",
 				"next": "Volgende",
 				"form": {