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

src/ClaudeDo.Localization/locales/de.json

@@ -288,9 +288,6 @@
       "binary": "Binärdatei — kein Text-Diff",
       "empty": "Kein Inhalt"
     },
-    "worktree": {
-      "title": "Worktree"
-    },
     "worktreesOverview": {
       "refresh": "Aktualisieren",
       "cleanupFinished": "Abgeschlossene aufräumen",
@@ -413,8 +410,6 @@
       "abort": "Diesen Merge abbrechen"
     },
     "diff": {
-      "windowTitle": "Planung — Kombiniertes Diff",
-      "modalTitle": "PLANUNG — KOMBINIERTES DIFF",
       "previewCombined": "Kombinierte Vorschau",
       "loading": "Wird geladen…"
     }