feat(ui): add auth pages, company rail, inbox redesign, and page improvements

Add Auth sign-in/sign-up page and InviteLanding page for invite acceptance.
Add CloudAccessGate that checks deployment mode and redirects to /auth when
session is required. Add CompanyRail with drag-and-drop company switching.
Add MarkdownBody prose renderer. Redesign Inbox with category filters and
inline join-request approval. Refactor AgentDetail to overview/configure/runs
views with claude-login support. Replace navigate() anti-patterns with <Link>
components in Dashboard and MetricCard. Add live-run indicators in sidebar
agents. Fix LiveUpdatesProvider cache key resolution for issue identifiers.
Add auth, health, and access API clients.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ui/src/api/index.ts

@@ -1,4 +1,7 @@
 export { api } from "./client";
+export { authApi } from "./auth";
+export { healthApi } from "./health";
+export { accessApi } from "./access";
 export { companiesApi } from "./companies";
 export { agentsApi } from "./agents";
 export { projectsApi } from "./projects";