feat(details): segmented Description/Steps/Files header

Replace the static DETAILS label and its dead space with a segment switcher; the card body now shows one section at a time. Step/file counts sit in the tab labels, the edit/preview toggle is scoped to Description, and drag-and-drop or add jumps to the Files tab. Tab labels localized (en/de).

src/ClaudeDo.Localization/locales/de.json

@@ -192,6 +192,11 @@
       "overLimitError": "Konnte {0} nicht hinzufügen: {1}",
       "invalidNameError": "Konnte {0} nicht hinzufügen: {1}",
       "selectIdleTask": "Zuerst eine inaktive Aufgabe auswählen"
+    },
+    "sections": {
+      "description": "Beschreibung",
+      "steps": "Schritte",
+      "files": "Dateien"
     }
   },
   "agent": {

src/ClaudeDo.Localization/locales/en.json

@@ -192,6 +192,11 @@
       "overLimitError": "Could not add {0}: {1}",
       "invalidNameError": "Could not add {0}: {1}",
       "selectIdleTask": "Select an idle task first"
+    },
+    "sections": {
+      "description": "Description",
+      "steps": "Steps",
+      "files": "Files"
     }
   },
   "agent": {