feat: Enhance real-time collaboration features with user awareness and document sharing

- Added user information (UserID, UserName, UserAvatar) to Client struct for presence tracking.
- Implemented failure handling in the broadcastMessage function to manage send failures and disconnect clients if necessary.
- Introduced document ownership and sharing capabilities:
  - Added OwnerID and Is_Public fields to Document model.
  - Created DocumentShare model for managing document sharing with permissions.
  - Implemented functions for creating, listing, and managing document shares in the Postgres store.
- Added user management functionality:
  - Created User model and associated functions for user management in the Postgres store.
  - Implemented session management with token hashing for security.
- Updated database schema with migrations for users, sessions, and document shares.
- Enhanced frontend Yjs integration with awareness event logging for user connections and disconnections.

backend/internal/models/document.go

@@ -14,14 +14,17 @@ const (
 )
 
 type Document struct {
-		ID        uuid.UUID    `json:"id"`
-  	Name      string       `json:"name"`
-  	Type      DocumentType `json:"type"`
-  	YjsState  []byte       `json:"-"` // Don't expose binary data in JSON
-  	CreatedAt time.Time    `json:"created_at"`
-  	UpdatedAt time.Time    `json:"updated_at"`
+    ID        uuid.UUID     `json:"id"`
+    Name      string        `json:"name"`
+    Type      DocumentType  `json:"type"`
+    YjsState  []byte        `json:"-"`
+    OwnerID   *uuid.UUID    `json:"owner_id"` // NEW
+    Is_Public bool          `json:"is_public"`
+    CreatedAt time.Time     `json:"created_at"`
+    UpdatedAt time.Time     `json:"updated_at"`
 }
 
+
 type CreateDocumentRequest struct {
   	Name string       `json:"name" binding:"required"`
   	Type DocumentType `json:"type" binding:"required"`