feat(native-chat): drop the standalone Chat session launcher

The QuickLaunch "Chat session" entry ("Start Codex without a terminal") was
scaffolding for testing the structured path, not a product surface. Shipping it
would introduce a second way to reach chat alongside the existing terminal
toggle, and then take it away again once the toggle routes codex to the
structured path — a surface that appears and disappears for exactly the
experimental users who would notice.

Structured chat now ships dormant: the store, journal, lease and app-server
transport are all present and exercised at startup, with no user-facing entry
point. The toggle users already know (right-click a codex tab -> Switch to chat
view, plus the pane menu, the pane shortcut, and the source-control surfaces)
becomes the single door in a follow-up, once a running CLI session can be
adopted into a structured one.

`useStructuredAgentSessionCreate` stays — adoption will call agentSession.create
through it. Only the menu entry and its now-unused imports go.

Verified: 1198 renderer tests, web typecheck, oxlint clean.

src/renderer/src/components/tab-bar/QuickLaunchButton.tsx

@@ -1,5 +1,5 @@
 import React, { useCallback } from 'react'
-import { MessageSquare, Settings as SettingsIcon } from 'lucide-react'
+import { Settings as SettingsIcon } from 'lucide-react'
 import { toast } from 'sonner'
 import { DropdownMenuItem, DropdownMenuShortcut } from '@/components/ui/dropdown-menu'
 import { getAgentCatalog, AgentIcon } from '@/lib/agent-catalog'
@@ -15,7 +15,6 @@ import {
   filterEnabledTuiAgents
 } from '../../../../shared/tui-agent-selection'
 import { translate } from '@/i18n/i18n'
-import { useStructuredAgentSessionCreate } from '../native-chat/use-structured-agent-session-create'
 
 export type QuickLaunchAgentMenuItemsProps = {
   worktreeId: string
@@ -117,7 +116,6 @@ function QuickLaunchAgentMenuItemsInner({
   const openSettingsPage = useAppStore((s) => s.openSettingsPage)
   const openSettingsTarget = useAppStore((s) => s.openSettingsTarget)
   const newAgentShortcut = useOptionalShortcutLabel('tab.newAgent')
-  const structuredSession = useStructuredAgentSessionCreate(worktreeId)
 
   const openAgentSettings = useCallback(() => {
     openSettingsTarget({ pane: 'agents', repoId: null })
@@ -218,35 +216,6 @@ function QuickLaunchAgentMenuItemsInner({
                 <DropdownMenuShortcut>{newAgentShortcut}</DropdownMenuShortcut>
               ) : null}
             </DropdownMenuItem>
-            {agent === 'codex' && structuredSession.supported ? (
-              <DropdownMenuItem
-                disabled={structuredSession.creating}
-                onSelect={() => {
-                  void structuredSession.create().catch((error) => {
-                    toast.error(
-                      translate(
-                        'auto.components.tab.bar.QuickLaunchButton.f378201fbd',
-                        'Could not create chat session'
-                      ),
-                      { description: error instanceof Error ? error.message : String(error) }
-                    )
-                  })
-                }}
-                className="gap-2 rounded-[7px] px-2 py-1.5 pl-6 text-[12px] leading-5 font-medium"
-                title={translate(
-                  'auto.components.tab.bar.QuickLaunchButton.a847779775',
-                  'Start Codex without a terminal'
-                )}
-              >
-                <MessageSquare className="size-3.5 text-muted-foreground" />
-                <span className="flex-1">
-                  {translate(
-                    'auto.components.tab.bar.QuickLaunchButton.0ea6a78efb',
-                    'Chat session'
-                  )}
-                </span>
-              </DropdownMenuItem>
-            ) : null}
           </React.Fragment>
         )
       })}