Harden production template validation and CI gates

[ChuanGz]

What changed

• centralize generated NuGet package versions
• make Swagger environment-aware and strengthen container validation
• add security scanning and CI runtime gates
• document template lifecycle, production-readiness boundaries, and roadmap evidence

Why

Improve production confidence while preserving the public template contract and keeping infrastructure reference implementations optional.

Validation

• M4 through M8 generation and build checks passed
• .NET 8 and .NET 10 generated projects build successfully
• Docker runtime validation is CI-only
• git diff check passed

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