ci: add centralized versioning with conventional commit bumps

- Add Directory.Build.props for consistent version across all projects
- Add version.json to track current version in source control
- Update release pipeline to:
  - Calculate version bumps from conventional commits
  - Pass /p:Version to all build/test/pack commands
  - Commit version.json back before tagging
  - Generate changelog in GitHub releases
- Version bump rules:
  - feat!: or BREAKING CHANGE: → major bump
  - feat: → minor bump
  - fix/perf/refactor/build/ci/docs/style/test: → patch bump

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Directory.Build.props

@@ -0,0 +1,26 @@
+<Project>
+  <!--
+    Centralized version management for all projects.
+    Version is set by CI via /p:Version parameter, or defaults to 0.0.0-local for local builds.
+    This ensures all assemblies and packages have consistent versioning.
+  -->
+  <PropertyGroup>
+    <!-- Default version for local development builds -->
+    <Version Condition="'$(Version)' == ''">0.0.0-local</Version>
+
+    <!-- Extract major.minor.patch for AssemblyVersion (doesn't support prerelease tags) -->
+    <_VersionPrefix>$([System.Text.RegularExpressions.Regex]::Match($(Version), '^\d+\.\d+\.\d+').Value)</_VersionPrefix>
+    <_VersionPrefix Condition="'$(_VersionPrefix)' == ''">0.0.0</_VersionPrefix>
+
+    <!-- Apply version to all version-related properties -->
+    <AssemblyVersion>$(_VersionPrefix).0</AssemblyVersion>
+    <FileVersion>$(_VersionPrefix).0</FileVersion>
+    <InformationalVersion>$(Version)</InformationalVersion>
+    <PackageVersion>$(Version)</PackageVersion>
+
+    <!-- Common properties for all projects -->
+    <LangVersion>latest</LangVersion>
+    <TreatWarningsAsErrors>false</TreatWarningsAsErrors>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+</Project>