feat: configure supervisor model and story graph use per conversation

Add a supervisor text-model selector using existing connections and a per-conversation story graph switch above knowledge settings. Hide the switch when Supervisor is disabled and enforce conversation preferences at local and remote tool execution boundaries.

Release note: Choose a dedicated supervisor model and control whether each conversation can query existing stories and experiences. Enabling graph access does not start a review or automatically insert context.

src/preload/index.ts

@@ -1135,6 +1135,9 @@ const desktopApi: DesktopApi = {
     setPinned: async (input) => {
       await ipcRenderer.invoke(ipcChannels.conversationsSetPinned, input)
     },
+    setStoryGraph: async (input) => {
+      await ipcRenderer.invoke(ipcChannels.conversationsSetStoryGraph, input)
+    },
     branchLocal: (input: ConversationBranchInput) =>
       ipcRenderer.invoke(
         ipcChannels.conversationsBranchLocal,