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/components/MarkdownBody.tsx

@@ -0,0 +1,21 @@
+import Markdown from "react-markdown";
+import remarkGfm from "remark-gfm";
+import { cn } from "../lib/utils";
+
+interface MarkdownBodyProps {
+  children: string;
+  className?: string;
+}
+
+export function MarkdownBody({ children, className }: MarkdownBodyProps) {
+  return (
+    <div
+      className={cn(
+        "prose prose-sm prose-invert max-w-none prose-p:my-1 prose-ul:my-1 prose-ol:my-1 prose-li:my-0 prose-pre:my-2 prose-headings:my-2 prose-headings:text-sm prose-table:my-2 prose-th:px-3 prose-th:py-1.5 prose-td:px-3 prose-td:py-1.5",
+        className,
+      )}
+    >
+      <Markdown remarkPlugins={[remarkGfm]}>{children}</Markdown>
+    </div>
+  );
+}