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.

tests/overlay-layering.electron.test.ts

@@ -40,6 +40,7 @@ it('keeps menus and notifications interactive above real Electron modals', async
 }, 120000)
 
 it.each([
+  ['saves the conversation story graph switch from App through production IPC and revokes existing tools', 'story-graph-switch-main.ts'],
   ['opens the MCP editor from App settings with native browser isolation and real persistence', 'mcp-overlay-main.ts'],
   ['keeps nested previews, sandbox keyboard, project modals and native overlays usable', 'overlay-paths-main.ts']
 ])('%s', async (_name, entry) => {
@@ -93,6 +94,9 @@ it.each([
     if (entry === 'mcp-overlay-main.ts') {
       expect(result.persistedAfterReload).toBe(true)
       expect(result.scenarios).toHaveLength(4)
+    } else if (entry === 'story-graph-switch-main.ts') {
+      expect(result).toMatchObject({ persistedAfterReload: true, revokedExistingBinding: true, hiddenWhenDisabled: true })
+      expect(result.scenarios).toHaveLength(4)
     } else {
       expect(result).toMatchObject({ image: true, iframe: true, project: true, tooltip: true, citation: true })
     }