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.Localization/locales/en.json

@@ -406,6 +406,7 @@
     "binaryHint": "Binary files can't be merged here — abort and resolve them in your editor:",
     "prevConflict": "Previous conflict (Shift+F8)",
     "nextConflict": "Next conflict (F8)",
+    "conflictMap": "Conflicts in this file — click a marker to jump",
     "acceptOurs": "Add main",
     "acceptTheirs": "Add incoming",
     "removeOurs": "Remove main",