chore: add CODEOWNERS, Code of Conduct, CHANGELOG, Source Link, and workflow fixes

[Copilot]

Summary

Repository health improvements across 8 areas.

Changes

New files

• .github/CODEOWNERS – assigns @petesramek as owner of .github/, src/, and tests/
• CODE_OF_CONDUCT.md – Contributor Covenant 2.1 with "project maintainer" as enforcement contact
• CHANGELOG.md – minimal changelog that links to the GitHub Releases page

Workflow fixes (.github/workflows/pull-request.yml)

• Fix trailing-quote bug – removed stray ' from the dotnet-sdk-version parameter in the publish-development-package job
• Fix benchmark if condition – replaced invalid github.env.is_release context with needs.workflow-variables.outputs.is-release == 'true'; added workflow-variables to the benchmark job's needs so the output is available
• Add security job – new job that runs dotnet list src/PolylineAlgorithm/PolylineAlgorithm.csproj package --vulnerable --include-transitive after build; fails on non-zero exit

Source Link (Directory.Build.props)

• Added <EmbedUntrackedSources>true</EmbedUntrackedSources> and <DebugType>embedded</DebugType> to the first PropertyGroup
• Added Microsoft.SourceLink.GitHub version 8.* (no known vulnerabilities per GitHub Advisory Database) to the analyzer ItemGroup

Documentation (docs/local-development.md)

• Added "Required Repository Secrets and Variables" section listing:
  • Secret: NUGET_PACKAGE_FEED_API_KEY
  • Variables: NUGET_PACKAGE_FEED_URL, BENCHMARKDOTNET_RUN_OVERRIDE, BENCHMARKDOTNET_RUNTIMES, BENCHMARKDOTNET_FILTER, DEFAULT_BUILD_FRAMEWORK, SRC_DEFAULT_GLOB_PATTERN

Verification

• dotnet build PolylineAlgorithm.slnx --configuration Release passes with 0 errors
• CodeQL security scan: 0 alerts