docs: merge notification system docs into single Native-First guide

- Consolidate 5 notification-system-* files into doc/notification-system.md
- Add web-push cleanup guide and Start-on-Login glossary entry
- Configure markdownlint for consistent formatting
- Remove web-push references, focus on native OS scheduling

Reduces maintenance overhead while preserving all essential information
in a single, well-formatted reference document.

src/utils/seedPhraseReminder.ts

@@ -0,0 +1,90 @@
+import { NotificationIface } from "@/constants/app";
+
+const SEED_REMINDER_KEY = "seedPhraseReminderLastShown";
+const REMINDER_COOLDOWN_MS = 24 * 60 * 60 * 1000; // 24 hours in milliseconds
+
+/**
+ * Checks if the seed phrase backup reminder should be shown
+ * @param hasBackedUpSeed - Whether the user has backed up their seed phrase
+ * @returns true if the reminder should be shown, false otherwise
+ */
+export function shouldShowSeedReminder(hasBackedUpSeed: boolean): boolean {
+  // Don't show if user has already backed up
+  if (hasBackedUpSeed) {
+    return false;
+  }
+
+  // Check localStorage for last shown time
+  const lastShown = localStorage.getItem(SEED_REMINDER_KEY);
+  if (!lastShown) {
+    return true; // First time, show the reminder
+  }
+
+  try {
+    const lastShownTime = parseInt(lastShown, 10);
+    const now = Date.now();
+    const timeSinceLastShown = now - lastShownTime;
+
+    // Show if more than 24 hours have passed
+    return timeSinceLastShown >= REMINDER_COOLDOWN_MS;
+  } catch (error) {
+    // If there's an error parsing the timestamp, show the reminder
+    return true;
+  }
+}
+
+/**
+ * Marks the seed phrase reminder as shown by updating localStorage
+ */
+export function markSeedReminderShown(): void {
+  localStorage.setItem(SEED_REMINDER_KEY, Date.now().toString());
+}
+
+/**
+ * Creates the seed phrase backup reminder notification
+ * @returns NotificationIface configuration for the reminder modal
+ */
+export function createSeedReminderNotification(): NotificationIface {
+  return {
+    group: "modal",
+    type: "confirm",
+    title: "Backup Your Identifier Seed?",
+    text: "It looks like you haven't backed up your identifier seed yet. It's important to back it up as soon as possible to secure your identity.",
+    yesText: "Backup Identifier Seed",
+    noText: "Remind me Later",
+    onYes: async () => {
+      // Navigate to seed backup page
+      window.location.href = "/seed-backup";
+    },
+    onNo: async () => {
+      // Mark as shown so it won't appear again for 24 hours
+      markSeedReminderShown();
+    },
+    onCancel: async () => {
+      // Mark as shown so it won't appear again for 24 hours
+      markSeedReminderShown();
+    },
+  };
+}
+
+/**
+ * Shows the seed phrase backup reminder if conditions are met
+ * @param hasBackedUpSeed - Whether the user has backed up their seed phrase
+ * @param notifyFunction - Function to show notifications
+ * @returns true if the reminder was shown, false otherwise
+ */
+export function showSeedPhraseReminder(
+  hasBackedUpSeed: boolean,
+  notifyFunction: (notification: NotificationIface, timeout?: number) => void,
+): boolean {
+  if (shouldShowSeedReminder(hasBackedUpSeed)) {
+    const notification = createSeedReminderNotification();
+    // Add 1-second delay before showing the modal to allow success message to be visible
+    setTimeout(() => {
+      // Pass -1 as timeout to ensure modal stays open until user interaction
+      notifyFunction(notification, -1);
+    }, 1000);
+    return true;
+  }
+  return false;
+}