feat: Add role-level permissions for agent sharing people picker

- Add PEOPLE_PICKER permission type with VIEW_USERS and VIEW_GROUPS permissions
  - Create custom middleware for query-aware permission validation
  - Implement permission-based type filtering in PeoplePicker component
  - Hide people picker UI when user lacks permissions, show only public toggle
  - Support granular access: users-only, groups-only, or mixed search modes

api/server/routes/accessPermissions.js

@@ -8,6 +8,7 @@ const {
   searchPrincipals,
 } = require('~/server/controllers/PermissionsController');
 const { requireJwtAuth, checkBan, uaParser, canAccessResource } = require('~/server/middleware');
+const { checkPeoplePickerAccess } = require('~/server/middleware/checkPeoplePickerAccess');
 
 const router = express.Router();
 
@@ -25,7 +26,7 @@ router.use(uaParser);
  * GET /api/permissions/search-principals
  * Search for users and groups to grant permissions
  */
-router.get('/search-principals', searchPrincipals);
+router.get('/search-principals', checkPeoplePickerAccess, searchPrincipals);
 
 /**
  * GET /api/permissions/{resourceType}/roles