Get started: an A-to-Z onboarding checklist

A new "Get started" page (top of the sidebar) that detects setup progress from real data
and guides the full flow: model the org -> product identity -> connect a model (BYOK) ->
staff an AI seat -> fill the backlog -> review the first agent output. Each step shows
done/todo with a deep link, plus an overall progress bar.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/src/components/AppShell.tsx

@@ -13,6 +13,7 @@ import {
   LogOut,
   Network,
   Package,
+  Rocket,
   ShieldCheck,
   Sparkles,
   Users,
@@ -45,6 +46,7 @@ export function AppShell({ children }: { children: ReactNode }) {
         <Separator className="bg-sidebar-border" />
 
         <nav className="flex flex-1 flex-col gap-1 p-3">
+          <NavItem icon={Rocket} label="Get started" to="/start" />
           <NavItem icon={LayoutDashboard} label="Board" to="/" />
           <NavItem icon={Sparkles} label="Team" to="/team" />
           <NavItem icon={Inbox} label="Cartable" to="/cartable" />