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/auth/oauth.go

@@ -0,0 +1,32 @@
+package auth
+
+import (
+	"golang.org/x/oauth2"
+	"golang.org/x/oauth2/github"
+	"golang.org/x/oauth2/google"
+)
+
+// GetGoogleOAuthConfig returns Google OAuth2 config
+func GetGoogleOAuthConfig(clientID, clientSecret, redirectURL string) *oauth2.Config {
+    return &oauth2.Config{
+        ClientID:     clientID,
+        ClientSecret: clientSecret,
+        RedirectURL:  redirectURL,
+        Scopes: []string{
+            "https://www.googleapis.com/auth/userinfo.email",
+            "https://www.googleapis.com/auth/userinfo.profile",
+        },
+        Endpoint: google.Endpoint,
+    }
+}
+
+// GetGitHubOAuthConfig returns GitHub OAuth2 config
+func GetGitHubOAuthConfig(clientID, clientSecret, redirectURL string) *oauth2.Config {
+    return &oauth2.Config{
+        ClientID:     clientID,
+        ClientSecret: clientSecret,
+        RedirectURL:  redirectURL,
+        Scopes:       []string{"user:email"},
+        Endpoint:     github.Endpoint,
+    }
+}