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/SidebarProjects.tsx

@@ -70,7 +70,7 @@ export function SidebarProjects() {
           {visibleProjects.map((project: Project) => (
             <NavLink
               key={project.id}
-              to={`/projects/${project.id}`}
+              to={`/projects/${project.id}/issues`}
               onClick={() => {
                 if (isMobile) setSidebarOpen(false);
               }}