feat(merge): diff Merge opens the 3-pane editor + conflict overview ruler

- The Merge button in the Diff window now hands a conflicting merge to the in-app
  3-pane editor (MergeModal routes 'conflict' through RequestConflictResolution,
  the same seam Approve uses) instead of dead-ending on a conflict message.
- Add a conflict overview ruler right of the Result pane: a proportional map of
  every conflict in the file, recolored by resolved state, click a tick to jump —
  so conflicts are findable in long files without scrolling.
- New MergeResolvedEdgeBrush token + conflictMap en/de key. Ui 128 + Loc 16 green.

src/ClaudeDo.Ui/Views/Conflicts/ConflictResolverView.axaml

@@ -149,6 +149,9 @@
             <Border Classes="col-head" DockPanel.Dock="Top">
               <TextBlock Classes="eyebrow" Text="{loc:Tr conflictResolver.result}"/>
             </Border>
+            <Canvas Name="ConflictMap" DockPanel.Dock="Right" Width="13"
+                    Background="{DynamicResource Surface2Brush}"
+                    ToolTip.Tip="{loc:Tr conflictResolver.conflictMap}"/>
             <ae:TextEditor Name="ResultEditor" ShowLineNumbers="True"/>
           </DockPanel>
         </Border>