ci: restrict Dependabot to compatible updates

[AbubakarMahmood]

Summary

• ignore SemVer-major NuGet version updates for every dependency
• remove the unsupported NuGet dependency-type: development group filter
• constrain the Microsoft/Asp.Versioning group to minor and patch updates

Why

PR #53 grouped 20 packages, including breaking MudBlazor, OpenAPI, Npgsql, MediatR, FluentValidation, and test-tooling majors. Its build failed with 26 compile errors. GitHub's current Dependabot schema does not support dependency-type grouping for NuGet, so the intended test-only filter was ignored.

Security updates remain eligible; compatible minor/patch version proposals remain enabled.

Validation

• parsed .github/dependabot.yml with PyYAML
• asserted wildcard major ignore, bounded group update types, and removal of the invalid group
• git diff --check

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