Show thinking indicator between tool calls during streaming

Previously the typing indicator only showed during 'submitted' status
(before first token). Once streaming began, gaps between tool calls
had no visual feedback — user saw silence and thought AI stopped.

Now isThinking is true when:
- status is submitted (waiting for first token)
- status is streaming and last part is a completed tool call or
  step-start (AI deciding what to do next)

src/components/ChatPanel.vue

@@ -23,6 +23,21 @@ const debugCopied = ref(false)
 
 const messages = computed(() => chat.value?.messages ?? [])
 const status = computed(() => chat.value?.status ?? 'ready')
+const isThinking = computed(() => {
+  const s = status.value
+  if (s !== 'submitted' && s !== 'streaming') return false
+  if (messages.value.length === 0) return true
+  const last = messages.value[messages.value.length - 1]
+  if (last.role !== 'assistant') return true
+  const parts = last.parts
+  if (parts.length === 0) return true
+  const lastPart = parts[parts.length - 1] as Record<string, unknown>
+  if (lastPart.type === 'step-start') return true
+  if ('toolCallId' in lastPart && lastPart.state === 'output-available') return true
+  if ('toolCallId' in lastPart && lastPart.state === 'output-error') return true
+  return s === 'submitted'
+})
+
 const showContinue = computed(() => {
   if (status.value !== 'ready') return false
   if (messages.value.length === 0) return false
@@ -87,9 +102,9 @@ function handleClearChat() {
           <div v-else data-test-id="chat-messages" class="flex flex-col gap-3">
             <ChatMessage v-for="msg in messages" :key="msg.id" :message="msg" />
 
-            <!-- Typing indicator -->
+            <!-- Thinking indicator: shown when AI is working but no visible activity -->
             <div
-              v-if="status === 'submitted'"
+              v-if="isThinking"
               data-test-id="chat-typing-indicator"
               class="flex gap-2"
             >