style(frontend): tidy drawer review nits

- RawSegmentsPanel: summary now reads 'Show N raw segments' for
  non-empty (with singular pluralization). The previous identical
  ternary branches read as a bug.
- PartiesGrid: replace the verbose intersection cast on AddressBlock
  with a direct ClaimDetailAddress cast (the union's other arm is
  Record<string, never>, ruled out by isEmptyAddress above).

src/components/ClaimDrawer/RawSegmentsPanel.tsx

@@ -44,8 +44,8 @@ export function RawSegmentsPanel({ rawSegments }: RawSegmentsPanelProps) {
           data-testid="raw-segments-summary"
         >
           {rawSegments.length === 0
-            ? "Show raw segments"
-            : "Show raw segments"}
+            ? `Show raw segments`
+            : `Show ${rawSegments.length} raw segment${rawSegments.length === 1 ? "" : "s"}`}
         </summary>
 
         {rawSegments.length === 0 ? (