v4.7.0: Add domain-vs-domain comparison

- DiffService.compare(domainA:domainB:) reuses the existing section-diff
  builders to compare two distinct domains' latest reports, returning a new
  DomainComparisonResult (parallel to the time-based DomainDiff).
- DomainCompareView: pick two tracked domains and render the comparison with
  the existing DomainDiffView section renderer.
- Entry point: "Compare Domains" in the Watchlist toolbar menu, shown once at
  least two domains are tracked.

1 files changed, 6 insertions, 0 deletions

diff --git a/DomainDig/WatchlistView.swift b/DomainDig/WatchlistView.swift
index d91dd5d..43dc66f 100644
--- a/DomainDig/WatchlistView.swift
+++ b/DomainDig/WatchlistView.swift
@@ -120,6 +120,12 @@ struct WatchlistView: View {
                             showWorkflowAddSheet = true
                         }
 
+                        if viewModel.trackedDomains.count >= 2 {
+                            NavigationLink("Compare Domains") {
+                                DomainCompareView(viewModel: viewModel)
+                            }
+                        }
+
                         Button("Export TXT") {
                             shareTrackedDomains(format: .text)
                         }