Fix: Complete WOPI integration - resolve all compilation errors

Go backend:
- Clean up corrupted wopi.go file (remove duplicate struct definitions)
- Remove duplicate UpdateFileSize method declaration

Flutter frontend:
- Fix SessionLoaded reference - use default base URL instead
- Replace AppTheme.primary with AppTheme.accentColor
- Remove unused local variables from file_browser_bloc

go_cloud/internal/models/wopi.go

@@ -115,10 +115,6 @@ type WOPISessionResponse struct {
 
 
 
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