FE-CAL-001/002/003: Add Calendar page with daily slot view and plans tab

- New CalendarPage with daily view (date navigation, slot list) and plans tab
- Route /calendar added in App.tsx
- Sidebar entry added after Proposals
- Daily view: shows time slots with type, status, priority, duration, event data
- Distinguishes real vs virtual (plan) slots visually
- Plans tab: shows schedule plan rules with schedule parameters

src/components/Sidebar.tsx

@@ -33,6 +33,7 @@ export default function Sidebar({ user, onLogout }: Props) {
     { to: '/', icon: '📊', label: 'Dashboard' },
     { to: '/projects', icon: '📁', label: 'Projects' },
     { to: '/proposals', icon: '💡', label: 'Proposals' },
+    { to: '/calendar', icon: '📅', label: 'Calendar' },
     { to: '/notifications', icon: '🔔', label: 'Notifications' + (unreadCount > 0 ? ' (' + unreadCount + ')' : '') },
     { to: '/monitor', icon: '📡', label: 'Monitor' },
     ...(user.is_admin ? [