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/onboarding.ejs

@@ -38,7 +38,7 @@
 	async function acceptTos() {
 		var checkbox = document.getElementById('tosCheckbox');
 		if (!checkbox.checked) {
-			alert('Please read and check the box to accept the Terms of Service.');
+			app.messages.toast('Please read and check the box to accept the Terms of Service.', 'danger');
 			return;
 		}
 		try {
@@ -50,14 +50,14 @@
 			document.getElementById('section-tos').style.display = 'none';
 			checkAllDone();
 		} catch(e) {
-			alert('Could not save TOS acceptance. Please try again.');
+			app.messages.toast('Could not save TOS acceptance. Please try again.', 'danger');
 		}
 	}
 
 	async function saveDob() {
 		var dob = document.getElementById('dobInput').value;
 		if (!dob) {
-			alert('Please enter your date of birth.');
+			app.messages.toast('Please enter your date of birth.', 'danger');
 			return;
 		}
 		try {
@@ -73,7 +73,7 @@
 			document.getElementById('section-dob').style.display = 'none';
 			checkAllDone();
 		} catch(e) {
-			alert('Could not save date of birth. Please try again.');
+			app.messages.toast('Could not save date of birth. Please try again.', 'danger');
 		}
 	}
 
@@ -81,11 +81,11 @@
 		var pw  = document.getElementById('pwInput').value;
 		var pw2 = document.getElementById('pwInput2').value;
 		if (!pw || pw.length < 5) {
-			alert('Password must be at least 5 characters.');
+			app.messages.toast('Password must be at least 5 characters.', 'danger');
 			return;
 		}
 		if (pw !== pw2) {
-			alert('Passwords do not match.');
+			app.messages.toast('Passwords do not match.', 'danger');
 			return;
 		}
 		try {
@@ -101,7 +101,7 @@
 			document.getElementById('section-password').style.display = 'none';
 			checkAllDone();
 		} catch(e) {
-			alert('Could not change password. Please try again.');
+			app.messages.toast('Could not change password. Please try again.', 'danger');
 		}
 	}