feat(frontend): Implement SignalR client integration for real-time notifications

Add comprehensive SignalR client implementation with connection management,
React hooks, and UI components for real-time notifications and project updates.

Changes:
- Install @microsoft/signalr package (v9.0.6)
- Create SignalR connection manager with auto-reconnect
- Implement useNotificationHub hook for notification hub
- Implement useProjectHub hook for project hub with room-based subscriptions
- Add NotificationPopover UI component with badge and dropdown
- Create Badge UI component
- Add SignalRProvider for global connection initialization
- Update Header to display real-time notifications
- Update app layout to include SignalRProvider
- Add comprehensive documentation in SIGNALR_INTEGRATION.md

Features:
- JWT authentication with automatic token management
- Auto-reconnect with exponential backoff (0s, 2s, 5s, 10s, 30s)
- Connection state management and indicators
- Real-time notification push
- Project event subscriptions (create, update, delete, status change)
- Room-based project subscriptions
- Typing indicators support

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

components/ui/badge.tsx

@@ -0,0 +1,36 @@
+import * as React from 'react';
+import { cva, type VariantProps } from 'class-variance-authority';
+
+import { cn } from '@/lib/utils';
+
+const badgeVariants = cva(
+  'inline-flex items-center rounded-full border px-2.5 py-0.5 text-xs font-semibold transition-colors focus:outline-none focus:ring-2 focus:ring-ring focus:ring-offset-2',
+  {
+    variants: {
+      variant: {
+        default:
+          'border-transparent bg-primary text-primary-foreground hover:bg-primary/80',
+        secondary:
+          'border-transparent bg-secondary text-secondary-foreground hover:bg-secondary/80',
+        destructive:
+          'border-transparent bg-destructive text-destructive-foreground hover:bg-destructive/80',
+        outline: 'text-foreground',
+      },
+    },
+    defaultVariants: {
+      variant: 'default',
+    },
+  }
+);
+
+export interface BadgeProps
+  extends React.HTMLAttributes<HTMLDivElement>,
+    VariantProps<typeof badgeVariants> {}
+
+function Badge({ className, variant, ...props }: BadgeProps) {
+  return (
+    <div className={cn(badgeVariants({ variant }), className)} {...props} />
+  );
+}
+
+export { Badge, badgeVariants };