feat(tools): add update-quest tool, switch to Big Pickle (opencode/zen)

- update_quest: aggiorna stato/nome/descrizione missioni
- db: get_quest(), update_quest con nome+desc
- prompt: quest_id nel contesto, esempio nei tool examples
- Switch da deepseek-v4-flash (go) a big-pickle (zen) — gratuito

src/engine/tools.py

@@ -376,6 +376,39 @@ def award_xp(character_id: int, xp: int) -> ToolResult:
     }
 
 
+@tool
+def update_quest(quest_id: int, status: str = "active", name: str = "", description: str = "") -> ToolResult:
+    VALID_STATUSES = ["active", "completed", "failed"]
+    if status not in VALID_STATUSES:
+        return {
+            "success": False,
+            "tool": "update-quest",
+            "message": f"Status '{status}' non valido. Usa: {', '.join(VALID_STATUSES)}",
+        }
+    quest = storage.get_quest(quest_id)
+    if not quest:
+        return {"success": False, "tool": "update-quest", "message": f"Missione #{quest_id} non trovata."}
+
+    changed = []
+    if status != quest["status"]:
+        changed.append(f"stato: {quest['status']}→{status}")
+    if name and name != quest.get("name"):
+        changed.append(f"nome: {quest.get('name')}→{name}")
+    if description and description != quest.get("description"):
+        changed.append("descrizione aggiornata")
+
+    storage.update_quest(quest_id, status=status, name=name, description=description)
+    display_name = name or quest["name"]
+    return {
+        "success": True,
+        "tool": "update-quest",
+        "quest_id": quest_id,
+        "name": display_name,
+        "status": status,
+        "message": f"Missione '{display_name}' → {status}." + (f" ({', '.join(changed)})" if changed else ""),
+    }
+
+
 @tool
 def dm_override(command: str, params: dict | None = None) -> ToolResult:
     manual = {