refactor: Use ProjectRootElement instead of XDocument for consistency

Replace XDocument-based XML parsing with ProjectRootElement from
Microsoft.Build.Construction, matching the existing pattern used in
GenerateReadMeModule.cs. This provides a more idiomatic approach for
parsing MSBuild project files.

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

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

Author: thomhurst

src/ModularPipelines.Build/Modules/FindProjectDependenciesModule.cs

@@ -1,4 +1,4 @@
-using System.Xml.Linq;
+using Microsoft.Build.Construction;
 using Microsoft.Extensions.Logging;
 using ModularPipelines.Attributes;
 using ModularPipelines.Context;
@@ -10,24 +10,19 @@ namespace ModularPipelines.Build.Modules;
 [DependsOn<FindProjectsModule>]
 public class FindProjectDependenciesModule : Module<FindProjectDependenciesModule.ProjectDependencies>
 {
-    public override async Task<ProjectDependencies?> ExecuteAsync(IModuleContext context, CancellationToken cancellationToken)
+    public override Task<ProjectDependencies?> ExecuteAsync(IModuleContext context, CancellationToken cancellationToken)
     {
         var projects = context.GetModule<FindProjectsModule, IReadOnlyList<File>>();
 
         var dependencies = new List<File>();
 
         foreach (var file in projects.Value!)
         {
-            await using var stream = System.IO.File.OpenRead(file.Path);
-            var doc = await XDocument.LoadAsync(
-                stream,
-                LoadOptions.None,
-                cancellationToken);
+            var projectRootElement = ProjectRootElement.Open(file)!;
 
-            var projectReferences = doc.Descendants()
-                .Where(e => e.Name.LocalName == "ProjectReference")
-                .Select(e => e.Attribute("Include")?.Value)
-                .OfType<string>();
+            var projectReferences = projectRootElement.Items
+                .Where(i => i.ItemType == "ProjectReference")
+                .Select(i => i.Include);
 
             foreach (var reference in projectReferences)
             {
@@ -45,7 +40,7 @@ public class FindProjectDependenciesModule : Module<FindProjectDependenciesModul
 
         LogProjects(context, projectDependencies);
 
-        return projectDependencies;
+        return Task.FromResult<ProjectDependencies?>(projectDependencies);
     }
 
     private static void LogProjects(IModuleContext context, ProjectDependencies projectDependencies)