Feat: Add notification list panel for backup notification display

[Copilot]

Implements a slide-out notification panel that displays a history of notifications as a backup when OS notifications fail to show properly.

Features Added

Notification Panel Component

• Slides out from the right side with smooth animations
• Shows up to 50 recent notifications with timestamps
• Color-coded notification types:
  • 🔴 Live notifications (green border)
  • ⭕ Offline notifications (red border)
  • 🔮 Predictive notifications (yellow border)

Notification Management

• Stores notification history in memory using a new useNotificationStore composable
• Unread counter badge on the notification bell icon
• Interactive features: mark as read, mark all read, clear all notifications
• Automatic timestamp formatting (e.g., "2m ago", "1h ago")

Integration

• New notification button in the header with bell icon and unread badge
• Enhanced existing notification system to store notifications locally while maintaining OS notification functionality
• Graceful fallback when Tauri notifications aren't available (browser mode)

Technical Implementation

The solution adds minimal code with surgical precision:

• 2 new files: NotificationPanel.vue component and useNotificationStore.js composable
• Modified 3 existing files to integrate the panel and enhance notification storage
• Zero breaking changes to existing functionality
• Browser compatibility with mock store for development

The notification panel provides exactly what was requested: a reliable way to view notifications when the OS doesn't display them properly, with a clean interface that matches the existing app design.

Fixes #11.

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