Moves the six backend projects on disk into Core/ and Hosts/
subfolders, matching the solution folders already defined in
Musify.slnx, so the file explorer reflects the same layout as the
solution:
backend/Core/Musify.Domain
backend/Core/Musify.Application
backend/Core/Musify.Infrastructure
backend/Hosts/Musify.Api
backend/Hosts/Musify.Worker
backend/Hosts/Musify.StreamingGateway
Updates every reference to the old paths: ProjectReference entries in
Musify.Api.csproj and Musify.Worker.csproj, the three Dockerfiles,
deploy/scripts/migrate.ps1|sh, deploy/zitadel/provision.ps1,
deploy/up.ps1, deploy/README.md and docs/development.md. Also fixes a
stale Dockerfile comment pointing at a compose file that no longer
exists.
Verified with `dotnet build Musify.slnx` against the new layout.
Admin