M6 1908b: foreground reminder delivery + recurrence/snooze UI (frontend)

Completes 1908 without Web Push. While the app is open, due reminders now
actually surface; recurring reminders + snooze/done are manageable.

- reminders store (singleton): polls /api/notes/reminders every 45s while
  the app is open; each due reminder fires ONCE as a toast (with an "Open"
  action) and, if the user opts in, a page-context OS Notification — no
  service worker, no PWA. Silently primes a stale backlog on first load;
  only announces recently-due ones. AppShell starts/stops it.
- Editor reminder section: a Repeat picker (Does not repeat / Daily /
  Weekly / Monthly / Yearly) + Done (advances a recurring reminder / clears
  a one-off) + Snooze 1h/1d, shown when a reminder is set.
- RemindersView rebuilt as a chronological list: per row a due time +
  recurrence badge + Done / 1h / 1d, click to open; plus an "Enable
  notifications" opt-in and a note that background alerts come with native.
- Note type gains `recurrence`; notes store setRecurrence /
  completeReminder / snoozeReminder.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm

frontend/src/components/AppShell.vue

@@ -5,6 +5,7 @@ import { useSessionStore } from "../stores/session";
 import { useConfigStore } from "../stores/config";
 import { useLabelsStore } from "../stores/labels";
 import { useSavedFiltersStore, type SavedFilter } from "../stores/savedFilters";
+import { useReminderStore } from "../stores/reminders";
 import { useUiStore } from "../stores/ui";
 import CommandPalette from "./CommandPalette.vue";
 import Icon from "./Icon.vue";
@@ -19,6 +20,7 @@ const session = useSessionStore();
 const config = useConfigStore();
 const labels = useLabelsStore();
 const savedFilters = useSavedFiltersStore();
+const reminders = useReminderStore();
 const ui = useUiStore();
 
 async function removeView(f: SavedFilter) {
@@ -153,9 +155,13 @@ function onKeydown(e: KeyboardEvent) {
 onMounted(() => {
   if (!labels.loaded) void labels.load();
   if (!savedFilters.loaded) void savedFilters.load();
+  reminders.start(); // foreground reminder delivery while the app is open
   window.addEventListener("keydown", onKeydown);
 });
-onBeforeUnmount(() => window.removeEventListener("keydown", onKeydown));
+onBeforeUnmount(() => {
+  reminders.stop();
+  window.removeEventListener("keydown", onKeydown);
+});
 
 const currentLabelId = computed(() => (route.name === "label" ? String(route.params.id) : null));