refactor(diff): single DiffViewer replaces DiffModal + WorktreeModal + PlanningDiff

src/ClaudeDo.Localization/locales/en.json

@@ -288,9 +288,6 @@
       "binary": "Binary file — no text diff",
       "empty": "No content"
     },
-    "worktree": {
-      "title": "Worktree"
-    },
     "worktreesOverview": {
       "refresh": "Refresh",
       "cleanupFinished": "Cleanup finished",
@@ -413,8 +410,6 @@
       "abort": "Abort this merge"
     },
     "diff": {
-      "windowTitle": "Planning — Combined diff",
-      "modalTitle": "PLANNING — COMBINED DIFF",
       "previewCombined": "Preview combined",
       "loading": "Loading…"
     }