Bump version to 0.8.0-preview.1 (#1181)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: jeffhandley <1031940+jeffhandley@users.noreply.github.com>

Author: Copilot

src/Directory.Build.props

@@ -5,7 +5,7 @@
     <PackageProjectUrl>https://modelcontextprotocol.github.io/csharp-sdk</PackageProjectUrl>
     <RepositoryUrl>https://github.com/modelcontextprotocol/csharp-sdk</RepositoryUrl>
     <RepositoryType>git</RepositoryType>
-    <VersionPrefix>0.7.0</VersionPrefix>
+    <VersionPrefix>0.8.0</VersionPrefix>
     <VersionSuffix>preview.1</VersionSuffix>
     <Authors>ModelContextProtocol</Authors>
     <Copyright>© Anthropic and Contributors.</Copyright>