M3 reminders: notes.remind_at + Reminders view

- Migration 0010: notes.remind_at (nullable tz). PATCH accepts remind_at
  (ISO set / null clear); GET /api/notes/reminders (soonest first, non-trashed);
  serialize includes remind_at.
- Frontend: datetime util (local<->ISO, format, overdue); notes store setReminder;
  editor datetime-local picker + clear; card reminder chip (overdue = red);
  sidebar Reminders entry + /reminders view.

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

frontend/src/components/NoteCard.vue

@@ -5,6 +5,7 @@ import type { Note } from "../stores/notes";
 import Icon from "./Icon.vue";
 import LinkedText from "./LinkedText.vue";
 import NoteChecklist from "./NoteChecklist.vue";
+import { formatReminder, isOverdue } from "../notes/datetime";
 
 defineProps<{ note: Note; reorderable?: boolean }>();
 const emit = defineEmits<{
@@ -79,6 +80,31 @@ function cardClass(color: NoteColor): string {
       >
     </div>
 
+    <div v-if="note.remind_at" class="mt-2">
+      <span
+        class="inline-flex items-center gap-1 rounded-full px-2 py-0.5 text-xs"
+        :class="
+          isOverdue(note.remind_at)
+            ? 'bg-red-100 text-red-700 dark:bg-red-950/50 dark:text-red-300'
+            : 'bg-black/5 text-neutral-600 dark:bg-white/10 dark:text-neutral-300'
+        "
+      >
+        <svg
+          class="h-3 w-3"
+          viewBox="0 0 24 24"
+          fill="none"
+          stroke="currentColor"
+          stroke-width="2"
+          stroke-linecap="round"
+          stroke-linejoin="round"
+        >
+          <circle cx="12" cy="12" r="10" />
+          <polyline points="12 6 12 12 16 14" />
+        </svg>
+        {{ formatReminder(note.remind_at) }}
+      </span>
+    </div>
+
     <div
       class="mt-2 flex items-center justify-end gap-0.5 opacity-0 transition focus-within:opacity-100 group-hover:opacity-100"
     >