🚀 Major refactor: Reorganize project structure

- Move WebAPI/ → src/Backend/DiunaBI.WebAPI/
- Move Frontend/ → src/Frontend/
- Move Deployment/ → deploy/
- Add proper .NET 8 solution structure
- Add plugin architecture with DiunaBI.Plugins.Morska
- Clean

DiunaBI.sln

@@ -1,25 +0,0 @@
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-EndProject
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