Add a sun cream tip for hot days (high > 26°C)

Temp-based stand-in for the UV-index idea from earlier -- neither
provider is currently fetched for UV, so this reuses the same
highTemp value already computed for the jacket tip, just the other
direction. Mutually exclusive with jacket (a high can't be both
<12 and >26).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/pages/Display.tsx

@@ -1,5 +1,5 @@
 import { useEffect, useRef, useState } from 'react'
-import { CloudOff, Umbrella, Shirt } from 'lucide-react'
+import { CloudOff, Umbrella, Shirt, Sun } from 'lucide-react'
 import { fetchForecast, fetchDisplayConfig } from '../api'
 import { WeatherIcon } from '../lib/icons'
 import { PointMeta } from '../components/PointMeta'
@@ -14,6 +14,7 @@ const TIP_ICONS: Record<TipKey, typeof Umbrella> = {
   umbrella: Umbrella,
   'umbrella-soft': Umbrella,
   jacket: Shirt,
+  sun: Sun,
 }
 
 const POLL_MS = 5 * 60 * 1000 // client polls more often than the server's hourly

frontend/src/types.ts

@@ -23,7 +23,7 @@ export interface Astro {
   sunset: string | null
 }
 
-export type TipKey = 'umbrella' | 'umbrella-soft' | 'jacket'
+export type TipKey = 'umbrella' | 'umbrella-soft' | 'jacket' | 'sun'
 
 export interface Summary {
   headline: string        // "Scattered showers today", "Rain likely later", ...