feat(pilot): ChatTabStrip component — [Chat] [Script Builder ●]

Two-tab strip for the chat region. Parent controls mounting (strip only
appears when the fix needs a script drafted). Indicator dot signals
in-progress draft state. Tab switching via onChange callback; parent
handles display:none toggling so tab contents preserve state.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/components/pilot/ChatTabStrip.tsx

@@ -0,0 +1,79 @@
+/**
+ * ChatTabStrip — two-tab strip at the top of the chat region:
+ * [Chat]  [Script Builder ●]
+ *
+ * Visibility is controlled by the parent (AssistantChatPage) — this
+ * component renders whenever it's mounted. The parent decides whether
+ * to mount it based on fix state.
+ *
+ * Tab switching uses onChange; the parent toggles display:none on the
+ * tab contents so state is preserved across switches.
+ */
+import { cn } from '@/lib/utils'
+
+export type ChatTab = 'chat' | 'script_builder'
+
+export interface ChatTabStripProps {
+  active: ChatTab
+  onChange: (tab: ChatTab) => void
+  /** When true, shows the amber indicator dot on the Script Builder tab. */
+  scriptBuilderHasProgress?: boolean
+}
+
+export function ChatTabStrip({
+  active, onChange, scriptBuilderHasProgress,
+}: ChatTabStripProps) {
+  return (
+    <div
+      role="tablist"
+      className="flex gap-1 px-4 pt-2 border-b border-default bg-bg-sidebar"
+    >
+      <TabButton
+        label="Chat"
+        active={active === 'chat'}
+        onClick={() => onChange('chat')}
+      />
+      <TabButton
+        label="Script Builder"
+        active={active === 'script_builder'}
+        onClick={() => onChange('script_builder')}
+        indicator={scriptBuilderHasProgress}
+      />
+    </div>
+  )
+}
+
+function TabButton({
+  label, active, onClick, indicator,
+}: {
+  label: string
+  active: boolean
+  onClick: () => void
+  indicator?: boolean
+}) {
+  return (
+    <button
+      role="tab"
+      aria-selected={active}
+      onClick={onClick}
+      className={cn(
+        'relative px-3 py-[7px] text-[12.5px] font-medium rounded-t-md transition-colors',
+        'border-b-2 -mb-px',
+        active
+          ? 'text-heading border-accent bg-bg-page'
+          : 'text-muted-foreground border-transparent hover:text-primary hover:bg-white/[0.08]',
+      )}
+    >
+      {label}
+      {indicator && (
+        <span
+          role="img"
+          aria-label="unsaved progress"
+          className="ml-1.5 inline-block w-1.5 h-1.5 rounded-full bg-warning align-middle"
+        />
+      )}
+    </button>
+  )
+}
+
+export default ChatTabStrip