feat: Add task scheduling and reminders system

Add comprehensive scheduling functionality with reminder notifications:

- Add scheduledDate, scheduledTime, and reminderMinutes fields to ImmerseTask
- Add enableReminders and defaultReminderMinutes to plugin settings
- Implement reminder notification system with 30-second background checks
- Add overdue task detection with visual indicators
- Add native HTML5 date/time pickers in Quick Add and Edit modals
- Add reminder dropdown with 5/10/15/30/60 minute options
- Display scheduled date/time with blue badge (📅) in task list
- Show pulsing red "OVERDUE" badge (⚠️) for past-due tasks
- Add red left border highlight for overdue tasks
- Implement startup check for due/overdue tasks when plugin loads
- Show overdue notices when Obsidian opens if tasks are past due
- Play alert sounds for reminders (if sounds enabled)
- Track shown reminders to prevent duplicate notifications

styles.css

@@ -464,6 +464,33 @@
 	color: var(--ft-warning);
 }
 
+.immerse-schedule-badge {
+	padding: 2px 8px;
+	background: var(--ft-primary);
+	color: white;
+	border-radius: 4px;
+	font-size: 11px;
+	font-weight: 500;
+}
+
+.immerse-schedule-badge.overdue {
+	background: var(--ft-danger);
+	animation: pulse-overdue 2s ease-in-out infinite;
+}
+
+@keyframes pulse-overdue {
+	0%, 100% {
+		opacity: 1;
+	}
+	50% {
+		opacity: 0.7;
+	}
+}
+
+.immerse-task-item.overdue {
+	border-left: 3px solid var(--ft-danger);
+}
+
 /* Task Actions */
 .immerse-task-actions {
 	display: flex;