Fix: Resolve Go and Flutter compilation errors

Go backend:
- Fix WOPI models file (remove duplicate package declaration and syntax errors)
- Add GetOrgMember method to database as alias for GetUserMembership
- Add UpdateFileSize method to database
- Remove unused net/url import from wopi_handlers.go
- Fix field names in WOPI struct initializers (match JSON tags)

Flutter frontend:
- Remove webview_flutter import (use simpler placeholder for now)
- Fix _createWOPISession to safely access SessionBloc state
- Replace WebViewController usage with placeholder UI
- Remove unused _generateRandomHex methods from login/signup forms
- Add missing mimeType parameter to DocumentCapabilities in mock repository
- Remove unused local variables in file_browser_bloc

go_cloud/internal/http/wopi_handlers.go

@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"io"
 	"net/http"
-	"net/url"
 	"strings"
 	"sync"
 	"time"