[Sprint 3] Update Directory.Build.props with remaining PRD-required build properties

[mpaulosky]

Summary

PR #37 already added ManagePackageVersionsCentrally=true to Directory.Build.props. This issue covers the remaining properties required by the PRD that are not yet present.

Properties to Add

Add the following to Directory.Build.props (or verify they exist):

<LangVersion>latest</LangVersion>
<EnforceCodeStyleInBuild>true</EnforceCodeStyleInBuild>
<EnableNETAnalyzers>true</EnableNETAnalyzers>
<AnalysisMode>All</AnalysisMode>
<TreatWarningsAsErrors>true</TreatWarningsAsErrors>

Acceptance Criteria

• Directory.Build.props contains all PRD-required shared build properties
• Any new properties don't break the Release build
• No individual .csproj overrides conflict with the new properties
• dotnet build MyBlog.slnx --configuration Release passes

Context

• ManagePackageVersionsCentrally=true was added by PR Centralize NuGet package versions with Directory.Packages.props #37 — do NOT duplicate
• Base branch: sprint/1-foundation
• Working agent: Samwise (squad:samwise)

[github-actions]

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[github-actions]

📋 Assigned to Sam (Backend / .NET)

Issue: #32 — Update Directory.Build.props with remaining PRD-required build properties

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Sam, work on issue #32