Add weather caching, useless-tip redirect, clock widget, and IAM Bedrock auth

- Cache the latest fetched tomorrow weather and expose it via /api/system/weather/latest
- Add a header Clock widget showing date/time plus the cached weather summary
- Redirect useless-talk mentions from the weather bot to the useless-tips webhook
- Switch Bedrock auth from bearer token to standard IAM access key/secret

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

frontend/src/components/Clock.vue

@@ -0,0 +1,87 @@
+<script setup lang="ts">
+import { ref, onMounted, onUnmounted } from 'vue'
+
+interface LatestWeather {
+  weather: string
+  pop: number | null
+  judgement: string
+  reason: string
+  fetched_at: string
+}
+
+const now = ref(new Date())
+const weather = ref<LatestWeather | null>(null)
+let clockIntervalId: number | null = null
+let weatherIntervalId: number | null = null
+
+const formatDate = (date: Date) => {
+  const weekdays = ['日', '月', '火', '水', '木', '金', '土']
+  return `${date.getFullYear()}/${String(date.getMonth() + 1).padStart(2, '0')}/${String(date.getDate()).padStart(2, '0')} (${weekdays[date.getDay()]})`
+}
+
+const formatTime = (date: Date) => {
+  return `${String(date.getHours()).padStart(2, '0')}:${String(date.getMinutes()).padStart(2, '0')}:${String(date.getSeconds()).padStart(2, '0')}`
+}
+
+const formatFetchedAt = (iso: string) => {
+  const d = new Date(iso)
+  return `${String(d.getHours()).padStart(2, '0')}:${String(d.getMinutes()).padStart(2, '0')}時点`
+}
+
+const fetchWeather = async () => {
+  try {
+    const response = await fetch('/api/system/weather/latest')
+    const data = await response.json()
+    weather.value = data
+  } catch (error) {
+    console.error('Failed to fetch latest weather:', error)
+  }
+}
+
+onMounted(() => {
+  clockIntervalId = window.setInterval(() => {
+    now.value = new Date()
+  }, 1000)
+
+  fetchWeather()
+  weatherIntervalId = window.setInterval(fetchWeather, 60000)
+})
+
+onUnmounted(() => {
+  if (clockIntervalId) clearInterval(clockIntervalId)
+  if (weatherIntervalId) clearInterval(weatherIntervalId)
+})
+</script>
+
+<template>
+  <div class="clock">
+    <span class="date">{{ formatDate(now) }}</span>
+    <span class="time">{{ formatTime(now) }}</span>
+    <span v-if="weather" class="weather" :title="`${formatFetchedAt(weather.fetched_at)}取得`">
+      🌤️ 明日: {{ weather.weather }}
+      <template v-if="weather.pop !== null">（降水{{ weather.pop }}%）</template>
+      ・👕{{ weather.judgement }}
+    </span>
+  </div>
+</template>
+
+<style scoped>
+.clock {
+  display: flex;
+  align-items: baseline;
+  gap: 8px;
+  font-family: monospace;
+  font-size: 13px;
+  color: #aaa;
+}
+.time {
+  color: #eee;
+  font-weight: 600;
+}
+.weather {
+  color: #8bc8ff;
+  font-size: 12px;
+  border-left: 1px solid #444;
+  padding-left: 8px;
+}
+</style>