Phase 4: polish + deploy-ready — mobile nav, README, Docker validation

- Mobile bottom tab bar (icon tabs) with the top nav hidden on small screens;
  content padding so it never overlaps
- data: scripts run via bun (not tsx/node) so the oven/bun build image needs no
  node — fixes the Dockerfile data:build step
- README: features, data sources, dev/test/build/deploy, env vars
- Validated the production Docker image end-to-end: build succeeds (378MB),
  container serves /healthz, /api/snapshot (104 fixtures), /api/predictions
  (20k sims), the SPA with deep-link fallback, and the story dataset

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

src/app/RootLayout.tsx

@@ -1,17 +1,18 @@
 import { useEffect } from 'react';
 import { Link, Outlet } from '@tanstack/react-router';
-import { Moon, Sun, Trophy } from 'lucide-react';
+import { GitMerge, Moon, Radio, Sparkles, Sun, Table, TrendingUp, Trophy } from 'lucide-react';
+import type { LucideIcon } from 'lucide-react';
 import { useUiStore } from '@/stores/uiStore';
 import { useTournamentStore } from '@/stores/tournamentStore';
 import { cn } from '@/lib/cn';
 
-const NAV = [
-  { to: '/', label: 'Live', exact: true },
-  { to: '/groups', label: 'Groups', exact: false },
-  { to: '/bracket', label: 'Bracket', exact: false },
-  { to: '/predict', label: 'Predict', exact: false },
-  { to: '/story', label: 'Story', exact: false },
-] as const;
+const NAV: { to: string; label: string; exact: boolean; icon: LucideIcon }[] = [
+  { to: '/', label: 'Live', exact: true, icon: Radio },
+  { to: '/groups', label: 'Groups', exact: false, icon: Table },
+  { to: '/bracket', label: 'Bracket', exact: false, icon: GitMerge },
+  { to: '/predict', label: 'Predict', exact: false, icon: TrendingUp },
+  { to: '/story', label: 'Story', exact: false, icon: Sparkles },
+];
 
 function ConnectionStatus() {
   const status = useTournamentStore((s) => s.status);
@@ -68,7 +69,7 @@ export function RootLayout() {
             </span>
             Cup<span className="text-accent">26</span>
           </Link>
-          <nav className="flex items-center gap-0.5 overflow-x-auto">
+          <nav className="hidden items-center gap-0.5 sm:flex">
             {NAV.map((item) => (
               <Link
                 key={item.to}
@@ -90,11 +91,29 @@ export function RootLayout() {
         </div>
       </header>
 
-      <main className="mx-auto w-full max-w-6xl flex-1 px-4 py-6">
+      <main className="mx-auto w-full max-w-6xl flex-1 px-4 py-6 pb-24 sm:pb-6">
         <Outlet />
       </main>
 
-      <footer className="border-t border-line py-6 text-center text-xs text-faint">
+      {/* Mobile bottom tab bar */}
+      <nav className="fixed inset-x-0 bottom-0 z-30 flex border-t border-line bg-surface/95 backdrop-blur sm:hidden">
+        {NAV.map((item) => (
+          <Link
+            key={item.to}
+            to={item.to}
+            {...(item.exact ? { activeOptions: { exact: true } } : {})}
+            className={cn(
+              'flex flex-1 flex-col items-center gap-0.5 py-2 text-[10px] font-medium text-muted',
+              '[&.active]:text-accent',
+            )}
+          >
+            <item.icon size={18} />
+            {item.label}
+          </Link>
+        ))}
+      </nav>
+
+      <footer className="border-t border-line py-6 pb-24 text-center text-xs text-faint sm:pb-6">
         <p>
           Cup26 · World Cup 2026 · data from openfootball, football-data.org &amp; StatsBomb open data ·
           model-driven odds, not betting advice