chore(code-quality): enforce dotnet formatting and analysis

[withakay]

Why

The SDK had inconsistent implicit build, formatting, analyzer, and contributor
workflow rules. Formatting also needed to be deterministic and applied before
commits without requiring developers to manually re-stage formatter changes.

What Changed

• Added repository-wide nullable, analyzer, code-style, naming, and
  warnings-as-errors policy.
• Added pinned CSharpier 1.3.0 and kept dotnet format for analyzer fixes.
• Added prek-based pre-commit verification with a Git wrapper that formats and
  re-stages staged C# files before prek runs.
• Added Worktrunk project hooks for pre-commit formatting and pre-merge checks.
• Pinned the .NET SDK and documented the SDK contributor style guide.
• Standardized CI and local checks on Release builds and formatting gates.
• Updated existing code and examples to conform to the enforced rules.

Validation

• mise run check
• Release build: 0 warnings, 0 errors
• 33 tests passed
• All file-based examples built successfully