fix: TypeScript null safety fixes for strict mode

- RateAnalysis: null guard on price_incl in timeline trace
- Layout: explicit null check on alertCount, use ?? for user.name

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

frontend/src/components/Layout.tsx

@@ -39,7 +39,7 @@ export default function Layout({ children }: { children: ReactNode }) {
             <NavLink key={to} to={to} className={({ isActive }) => isActive ? 'active' : ''}>
               <Icon {...ICON} />
               {label}
-              {to === '/market' && alertCount ? (
+              {to === '/market' && alertCount != null && alertCount > 0 ? (
                 <span style={{
                   marginLeft: 'auto', background: 'var(--danger)', color: '#fff',
                   borderRadius: 10, fontSize: 10, fontWeight: 700,
@@ -49,7 +49,7 @@ export default function Layout({ children }: { children: ReactNode }) {
             </NavLink>
           ))}
         </nav>
-        <div className="sidebar-user">{user.name || user.email}</div>
+        <div className="sidebar-user">{user.name ?? user.email}</div>
       </aside>
 
       <header className="top-bar">

frontend/src/pages/RateAnalysis.tsx

@@ -354,7 +354,7 @@ function buildTimelineTraces(entries: TimelineEntry[]) {
     mode: 'lines+markers' as const,
     name: room,
     x: pts.map(p => p.scraped_at),
-    y: pts.map(p => p.price_incl),
+    y: pts.map(p => p.price_incl ?? null),
     line: { color: colors[i % colors.length], width: 2 },
     marker: { size: 5, color: colors[i % colors.length] },
     hovertemplate: `${room}: £%{y:.2f}<extra></extra>`,