feat: Add PathViewer and RiskDriftCard components with templates and styles

- Implemented PathViewerComponent for visualizing reachability call paths.
- Added RiskDriftCardComponent to display reachability drift results.
- Created corresponding HTML templates and SCSS styles for both components.
- Introduced test fixtures for reachability analysis in JSON format.
- Enhanced user interaction with collapsible and expandable features in PathViewer.
- Included risk trend visualization and summary metrics in RiskDriftCard.

src/Scanner/__Tests/StellaOps.Scanner.Reachability.Tests/RichGraphWriterTests.cs

@@ -132,6 +132,6 @@ public class RichGraphWriterTests
         
         // Verify meta.json also contains the blake3-prefixed hash
         var metaJson = await File.ReadAllTextAsync(result.MetaPath);
-        Assert.Contains("\"graph_hash\":\"blake3:", metaJson);
+        Assert.Contains("\"graph_hash\": \"blake3:", metaJson);
     }
 }