build: add csharpier tooling

[mnbuhl]

Summary

• Pin CSharpier as a local .NET tool so contributors use the same formatter version.
• Add a CSharpier ignore file for EF Core generated migration output.
• Add CI coverage so formatting is checked in pull requests.

Changes

• Added .config/dotnet-tools.json with CSharpier 1.2.6.
• Added .csharpierignore for **/Migrations/**.
• Updated the verify workflow to restore .NET tools and run dotnet csharpier check ..
• Applied the current CSharpier formatting output to two existing C# files.

Risk and rollout

• Low risk: this is tooling and formatting only, with no intended runtime behavior change.
• CI now fails on unformatted C# changes, so formatter drift is caught before merge.
• No Git hooks are added or required.

Notes for reviewers

• The formatting gate lives in CI; local formatting remains an explicit dotnet csharpier format . command.

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[github-actions]

Package	Line Rate	Health
Atomizer	72%	➖
Atomizer	72%	➖
Atomizer	14%	❌
Atomizer.EntityFrameworkCore	90%	✔
Atomizer	14%	❌
Atomizer.EntityFrameworkCore	90%	✔
Atomizer	14%	❌
Atomizer.EntityFrameworkCore	90%	✔
Atomizer	72%	➖
Summary	60% (7347 / 13050)	➖