Remove all native alert()/confirm() calls

Native confirm() dialogs block browser automation entirely (discovered
via a frozen tab while browser-testing the app.messages/app.modal
adoption), and native alert()/confirm() are visually inconsistent with
the rest of the UI. Replaced every call site with
app.messages.action/confirm/toast:

- directory.ejs: rotateSecret/deleteResource confirms and all inline
  save/add/remove-group/edge error alerts now target #resourceModal's
  actionMessage (or, for deleteResource — called from the outer table
  row, not the modal — the page's own card).
- impersonate_modal.ejs, onboarding.ejs: no local .actionMessage target
  exists on these pages, so their alerts became page-wide toasts.
- executive.ejs: two alerts in sendNotification's validation now use the
  existing $compose target; saveTos's alert now reuses the function's
  own msgEl inline-message element instead of introducing a second
  mechanism.
- users.ejs, profile.ejs, proxy's profile.ejs: toggleActive's alert
  (no row context available at the call site) became a toast;
  revokeInvite/revokeToken/rotateToken use the row/card element already
  in scope.
- app.js: removed app.user.remove and app.oauthClient.remove, which
  contained native confirm() guards and had zero callers anywhere in the
  app — dead code, deleted rather than converted.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

nodejs/views/impersonate_modal.ejs

@@ -68,7 +68,7 @@
 function startImpersonate(uid){
 	app.impersonate.create(uid, function(error, data){
 		if(error){
-			alert('Could not start impersonation: ' + (data && data.message ? data.message : 'Unknown error'));
+			app.messages.toast('Could not start impersonation: ' + (data && data.message ? data.message : 'Unknown error'), 'danger');
 			return;
 		}
 		$('#impersonateModalTitle').text(data.uid);