feat: enhance frontend with new UI components and Tailwind CSS integration

- Added CreateButton and DocumentCard components for document management.
- Implemented tabbed interface for owned and shared documents in Home page.
- Integrated Tailwind CSS for styling and layout improvements.
- Introduced utility functions for class name management.
- Updated package.json with new dependencies for UI components and styling.
- Created PostCSS configuration for Tailwind CSS.
- Refactored Navbar and button components for better usability and design.
- Enhanced document API to include owner_id for document sharing functionality.

backend/internal/handlers/websocket.go

@@ -3,6 +3,7 @@ package handlers
 import (
 	"log"
 	"net/http"
+	"time"
 
 	"github.com/M1ngdaXie/realtime-collab/internal/auth"
 	"github.com/M1ngdaXie/realtime-collab/internal/config"
@@ -13,6 +14,10 @@ import (
 	"github.com/gorilla/websocket"
 )
 
+// connectionSem limits concurrent WebSocket connection handshakes
+// to prevent overwhelming the database during connection storms
+var connectionSem = make(chan struct{}, 200)
+
 type WebSocketHandler struct {
 	hub   *hub.Hub
 	store store.Store
@@ -44,6 +49,15 @@ func (wsh *WebSocketHandler) getUpgrader() websocket.Upgrader {
 }
 
 func (wsh *WebSocketHandler) HandleWebSocket(c *gin.Context) {
+	// Acquire semaphore to limit concurrent connection handshakes
+	select {
+	case connectionSem <- struct{}{}:
+		defer func() { <-connectionSem }()
+	case <-time.After(10 * time.Second):
+		c.JSON(http.StatusServiceUnavailable, gin.H{"error": "server busy, retry later"})
+		return
+	}
+
 	roomID := c.Param("roomId")
 	if roomID == "" {
 		c.JSON(http.StatusBadRequest, gin.H{"error": "roomId is required"})