Add minimal stock listing app: actions, Postgres schema, stocks page, Claude Agent SDK harness

- Add stocks table (server/db) with list/get/add/update/delete actions, scoped
  per user, backing both the chat agent and the /stocks UI via
  useActionQuery/useActionMutation
- Add mobile-first /stocks page (shadcn table/cards, watchlist, search) and
  wire it into the sidebar, navigation state, and view-screen context
- Install the platform's Claude Agent SDK harness (server/plugins,
  server/routes/api/claude-agent) so the app agent runs on the platform's own
  Claude subscription instead of the Builder.io gateway; fix the vendored
  turn.post.ts route to resolve the session and wrap it in
  runWithRequestContext, since custom /api/ routes aren't auto-wrapped in
  request context the way /_agent-native/actions/* are
- Add shadcn table/badge/dialog/select components (Tabler icons, not lucide)

app/hooks/use-navigation-state.ts

@@ -39,6 +39,7 @@ function threadIdFromPath(pathname: string): string | null {
 
 function viewForPath(pathname: string): string {
   if (isChatPath(pathname)) return "chat";
+  if (pathname.startsWith("/stocks")) return "stocks";
   if (pathname.startsWith("/database")) return "database";
   if (pathname.startsWith("/extensions")) return "extensions";
   if (pathname.startsWith("/observability")) return "observability";
@@ -53,6 +54,8 @@ function pathForView(view?: string): string {
     case "home":
     case "ask":
       return "/";
+    case "stocks":
+      return "/stocks";
     case "database":
       return "/database";
     case "extensions":