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/i18n/en-US.ts

@@ -50,11 +50,13 @@ const messages = {
     observability: "Observability",
     openNavigation: "Open navigation",
     settings: "Settings",
+    stocks: "Stocks",
     team: "Team",
   },
   pages: {
     databaseTitle: "Database",
     observabilityPageTitle: "Agent Observability",
+    stocksDescription: "Track tickers, prices, and your watchlist.",
     teamTitle: "Team",
     teamCreateOrgDescription:
       "Create an organization to invite teammates and share this app.",