dashboard: theme all remaining dialogs (replace native confirm/alert/prompt)

Follow-up to the themed-modal component: route every remaining native
browser dialog through modal.js so nothing falls back to the OS chrome.

- modal.js: add themedPrompt (input dialog) + themedToast (non-blocking
  transient notification, info/error/ok) alongside openDialog/themedConfirm.
- Migrate call sites: bindAsyncForms confirm/prompt/alerts (common.js),
  the answer-validation alert (call.js), the M0V3 reparent confirm + action
  toasts (tabs.js), and the schedule form/cancel/fire confirms + validation
  and error alerts (schedules.js).
- UX: blocking modal for confirms/prompts; non-blocking toast for transient
  errors + validation. Destructive confirms keep the danger styling.
- CSS for the toast stack + prompt input.

common.js <-> modal.js is a safe deferred import cycle (usage is call-time
only); esbuild bundles it clean.

frontend/packages/dashboard/src/modal.js

@@ -123,3 +123,60 @@ export function themedConfirm(opts = {}) {
     return out;
   });
 }
+
+// themedPrompt({ title, message, label, placeholder, value, confirmLabel, cancelLabel })
+//   → Promise<string | null>. Themed replacement for window.prompt(): an input
+//   dialog that resolves to the entered string on confirm, or null on cancel.
+export function themedPrompt(opts = {}) {
+  const {
+    title = '', message = '', label = '', placeholder = '', value = '',
+    confirmLabel = 'ok', cancelLabel = 'cancel',
+  } = opts;
+  const input = el('input', { type: 'text', class: 'tc-input', placeholder });
+  if (value) input.value = value;
+  const content = el('div', { class: 'tc-promptfield' },
+    label ? el('label', { class: 'tc-promptlabel' }, label) : null,
+    input);
+  const result = openDialog({
+    title,
+    message,
+    content,
+    buttons: [
+      { label: cancelLabel, value: '__cancel__', class: 'tc-cancel' },
+      { label: confirmLabel, value: '__ok__', class: 'tc-confirm', autofocus: true },
+    ],
+  }).then((v) => (v === '__ok__' ? input.value : null));
+  // Prefer focusing the field over the OK button once the dialog has mounted.
+  setTimeout(() => input.focus(), 0);
+  return result;
+}
+
+// themedToast(message, { type, duration }) — non-blocking transient
+//   notification; a lighter alternative to a modal for feedback that needs no
+//   decision (errors, validation, status). Stacks in a fixed top-right
+//   container, auto-dismisses after `duration` ms (errors linger longer), and
+//   can be clicked to dismiss early. `type` ∈ {'info','error','ok'}.
+export function themedToast(message, opts = {}) {
+  const { type = 'info', duration } = opts;
+  const ms = duration != null ? duration : (type === 'error' ? 8000 : 4000);
+  let container = document.getElementById('tc-toasts');
+  if (!container) {
+    container = el('div', { id: 'tc-toasts', class: 'tc-toasts' });
+    document.body.append(container);
+  }
+  const toast = el('div', {
+    class: 'tc-toast tc-toast-' + type,
+    role: type === 'error' ? 'alert' : 'status',
+  }, message);
+  let removed = false;
+  const remove = () => {
+    if (removed) return;
+    removed = true;
+    toast.classList.add('tc-toast-out');
+    setTimeout(() => toast.remove(), 200);
+  };
+  toast.addEventListener('click', remove);
+  container.append(toast);
+  if (ms > 0) setTimeout(remove, ms);
+  return toast;
+}