feat: add Script Builder page with chat UI, code blocks, preview modal, and save dialog

- ScriptCodeBlock: collapsed code preview with syntax highlighting (first 5 lines)
- ScriptBuilderInput: auto-resize chat input with Enter-to-send
- ScriptBuilderChat: message list with markdown rendering and code blocks
- ScriptPreviewModal: fullscreen script viewer with line numbers
- SaveToLibraryDialog: save script with name, description, category, team sharing
- ScriptBuilderPage: language selector, session management, FlowPilot handoff
- Added route, sidebar nav item (fuchsia), and mobile nav entry

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/router.tsx

@@ -52,6 +52,7 @@ const FlowPilotSessionPage = lazy(() => import('@/pages/FlowPilotSessionPage'))
 const EscalationQueuePage = lazy(() => import('@/pages/EscalationQueuePage'))
 const ReviewQueuePage = lazy(() => import('@/pages/ReviewQueuePage'))
 const FlowPilotAnalyticsPage = lazy(() => import('@/pages/FlowPilotAnalyticsPage'))
+const ScriptBuilderPage = lazy(() => import('@/pages/ScriptBuilderPage'))
 const KBAcceleratorPage = lazy(() => import('@/pages/KBAcceleratorPage'))
 const GuidesHubPage = lazy(() => import('@/pages/GuidesHubPage'))
 const GuideDetailPage = lazy(() => import('@/pages/GuideDetailPage'))
@@ -190,6 +191,7 @@ export const router = sentryCreateBrowserRouter([
       { path: 'step-library', element: page(StepLibraryPage) },
       { path: 'scripts', element: page(ScriptLibraryPage) },
       { path: 'scripts/manage', element: page(ScriptManagePage) },
+      { path: 'script-builder', element: page(ScriptBuilderPage) },
       { path: 'kb-accelerator', element: page(KBAcceleratorPage) },
       { path: 'assistant', element: page(AssistantChatPage) },
       { path: 'flow-assist', element: page(FlowAssistPage) },