feat(ui): Listen-Einstellungen — Checkbox fuer serialize_on_file_overlap

Das Flag war bisher nur ueber MCP set_list_config erreichbar. UpdateListConfigDto
fuehrt es tri-state (null = gespeicherten Wert behalten), damit nur das
Listen-Modal es setzen/loeschen kann und kein anderer Aufrufer es per Omission
verliert.

src/ClaudeDo.Localization/locales/en.json

@@ -371,6 +371,8 @@
       "manualListHint": "New tasks in this list start out manual: no queueing, running or refining, and automation skips them. You can still open a hand-driven session.",
       "findingsTracked": "Commit the .claudedo findings folder",
       "findingsTrackedHint": "Off: the folder stays out of git via .git/info/exclude. On: findings travel with the repo.",
+      "serializeOnFileOverlap": "Serialize tasks that touch the same files",
+      "serializeOnFileOverlapHint": "Off: tasks in this list run in parallel. On: a queued task whose declared file scope overlaps a running or awaiting-review sibling waits instead of starting.",
       "sectionAgent": "AGENT",
       "resetAgentSettings": "Reset agent settings",
       "sectionVerify": "VERIFICATION",