Fix: Quests now properly scoped per-chat

Quests were bleeding through from other chats because loadChatData()
wasn't resetting them when switching to a chat without RPG data.

When loading a chat with no rpg_companion metadata, the function now
resets quests to empty state (main: 'None', optional: []) along with
other tracker data. This ensures each chat maintains its own quest
state independently.

src/core/persistence.js

@@ -204,6 +204,10 @@ export function loadChatData() {
                     stored: {},
                     assets: "None"
                 }
+            },
+            quests: {
+                main: "None",
+                optional: []
             }
         });
         setLastGeneratedData({