fix(chat): remove manual finish button — sale auto-closes when the customer decides

The realistic sales simulation must not offer a "Finish practice / จบการฝึก"
button, because the chat is meant to auto-close on buy/walk/try (as originally
decided in ffb7cdd). The finish button and its chatFinish handler were
reintroduced in 3c22d88 and are now removed; the composer holds only Send and the
debrief renders automatically once the session finishes. Regression test asserts
no finish/summary button is rendered.

frontend/src/views/Chat.spec.js

@@ -55,6 +55,22 @@ describe('Chat resume state', () => {
     expect(wrapper.text()).not.toContain('เลือกสถานการณ์')
   })
 
+  it('does not render a manual finish/summary button — chat closes only on auto-close', async () => {
+    const { default: Chat } = await import('./Chat.vue')
+    const wrapper = mount(Chat, {
+      global: { stubs: { 'router-link': RouterLinkStub } },
+    })
+    await flushPromises()
+
+    // The sale simulation must auto-close (buy/walk/try); no "จบการฝึก"/"Finish practice"
+    // button should interrupt the realistic conversation.
+    expect(wrapper.find('.composer').exists()).toBe(true)
+    expect(wrapper.text()).not.toContain('Finish practice')
+    expect(wrapper.text()).not.toContain('จบการฝึก')
+    // Only the send control; no ghost finish button.
+    expect(wrapper.find('button.ghost').exists()).toBe(false)
+  })
+
   it('starts a hidden-group admin chat in preview mode', async () => {
     mocks.api.chatResume.mockRejectedValue(new Error('no active session'))
     mocks.api.mySessions.mockResolvedValue({ sessions: [] })

frontend/src/views/Chat.vue

@@ -72,9 +72,6 @@
       <div v-if="phase === 'chat'" class="composer">
         <input v-model="text" @keyup.enter="send" :disabled="sending" :placeholder="i18n.t('send')" />
         <button class="primary" @click="send" :disabled="sending || !text.trim()"><Send :size="16" :stroke-width="1.8" /> {{ i18n.t('send') }}</button>
-        <button class="ghost" @click="finish" :disabled="sending">
-          {{ i18n.locale === 'en' ? 'Finish practice' : 'จบการฝึก' }}
-        </button>
       </div>
 
       <!-- Debrief -->
@@ -161,22 +158,6 @@ async function begin() {
   }
 }
 
-async function finish() {
-  if (sending.value) return
-  sending.value = true
-  try {
-    const res = await api.chatFinish(gid, pid)
-    debrief.value = res.debrief || null
-    messages.value = res.session?.messages || messages.value
-    phase.value = 'done'
-    scrollDown()
-  } catch (e) {
-    alert(i18n.t('chatActionFailed'))
-  } finally {
-    sending.value = false
-  }
-}
-
 onMounted(async () => {
   persona.value = (await api.getPersona(gid, pid)).persona
   if (auth.isAdmin) {