Fix plan days with no chapters, add a way out of ink mode, harden ntfy reminders

Plans can no longer have more days than chapters (existing ones heal), and
opening a plan never strands the Reader on an empty day. The Reader shows
Done drawing while inking (Escape also exits). Reminders use the user's own
timezone, send within a 3 hour grace window, and Settings has a Send test
notification button.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/syncService.js

@@ -159,6 +159,11 @@ export async function changePassword(currentPassword, newPassword) {
   return request('POST', '/auth/change-password', { currentPassword, newPassword });
 }
 
+/** Sends a test notification to the given ntfy topic/server (or the saved ones). */
+export async function sendReminderTest(settings) {
+  return request('POST', '/auth/reminder-test', settings);
+}
+
 /** Sets the daily reading reminder sent via ntfy.sh ({ reminderEnabled, ntfyUrl, ntfyTopic, reminderTime }). */
 export async function updateReminderSettings(settings) {
   return request('PATCH', '/auth/reminder-settings', settings);