feat: temperature unit preference and slot timezone display for briefing

- Add °C/°F toggle in briefing settings; persisted in briefing_config.temp_unit
- briefing_pipeline reads temp_unit and converts Open-Meteo Celsius values
  before passing them to the LLM (both full compilation and slot injection)
- Scheduled Slots section now shows each UTC slot time converted to the
  user's browser local time, plus a line confirming which timezone the
  browser is using

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

frontend/src/api/client.ts

@@ -328,6 +328,7 @@ export interface BriefingConfig {
   work_days: number[];
   slots: BriefingSlots;
   notifications: boolean;
+  temp_unit: 'C' | 'F';
 }
 
 export interface BriefingFeed {
@@ -360,6 +361,7 @@ const DEFAULT_BRIEFING_CONFIG: BriefingConfig = {
   work_days: [1, 2, 3, 4, 5],
   slots: { compilation: true, morning: true, midday: false, afternoon: false },
   notifications: true,
+  temp_unit: 'C',
 };
 
 export async function getBriefingConfig(): Promise<BriefingConfig> {

frontend/src/views/SettingsView.vue

@@ -173,6 +173,18 @@ function toggleWorkDay(day: number) {
   days.sort();
 }
 
+/** Convert a UTC hour (0–23) to the browser's local time string, e.g. "6:00 am (UTC 4:00)" */
+function utcSlotToLocal(utcHour: number): string {
+  const now = new Date();
+  const utcMs = Date.UTC(now.getUTCFullYear(), now.getUTCMonth(), now.getUTCDate(), utcHour, 0, 0);
+  const local = new Date(utcMs);
+  const localStr = local.toLocaleTimeString([], { hour: 'numeric', minute: '2-digit' });
+  const utcStr = utcHour === 0 ? '12:00 am' : utcHour < 12
+    ? `${utcHour}:00 am`
+    : utcHour === 12 ? '12:00 pm' : `${utcHour - 12}:00 pm`;
+  return `${localStr} (UTC ${utcStr})`;
+}
+
 async function saveBriefingSettings() {
   briefingSaving.value = true;
   briefingSaved.value = false;
@@ -1316,6 +1328,22 @@ function formatUserDate(iso: string): string {
           </label>
           <p class="field-hint">Look up weather for locations in today's calendar events.</p>
         </div>
+
+        <div class="field" style="margin-top: 1rem">
+          <label class="field-label">Temperature unit</label>
+          <div class="briefing-unit-toggle">
+            <button
+              type="button"
+              :class="['briefing-unit-btn', { active: briefingConfig.temp_unit === 'C' }]"
+              @click="briefingConfig.temp_unit = 'C'"
+            >°C</button>
+            <button
+              type="button"
+              :class="['briefing-unit-btn', { active: briefingConfig.temp_unit === 'F' }]"
+              @click="briefingConfig.temp_unit = 'F'"
+            >°F</button>
+          </div>
+        </div>
       </section>
 
       <!-- Work schedule -->
@@ -1336,27 +1364,33 @@ function formatUserDate(iso: string): string {
       <!-- Slots -->
       <section class="settings-section full-width">
         <h2>Scheduled Slots</h2>
-        <p class="section-desc">Each active slot will post an update into your briefing conversation.</p>
+        <p class="section-desc">
+          Each active slot posts an update into your briefing conversation.
+          Slots run on the server in UTC — your local equivalent is shown below.
+        </p>
         <div class="briefing-slot-list">
           <div
-            v-for="[key, label, time] in ([
-              ['compilation', 'Morning briefing', '4:00 am'],
-              ['morning', 'Office check-in', '8:00 am'],
-              ['midday', 'Midday update', '12:00 pm'],
-              ['afternoon', 'End of day', '4:00 pm'],
+            v-for="[key, label, utcHour] in ([
+              ['compilation', 'Morning briefing', 4],
+              ['morning', 'Office check-in', 8],
+              ['midday', 'Midday update', 12],
+              ['afternoon', 'End of day', 16],
             ] as const)"
             :key="key"
             class="briefing-slot-row"
           >
             <div class="briefing-slot-info">
               <span class="briefing-slot-label">{{ label }}</span>
-              <span class="briefing-slot-time">{{ time }}</span>
+              <span class="briefing-slot-time">{{ utcSlotToLocal(utcHour) }}</span>
             </div>
             <label>
               <input type="checkbox" v-model="briefingConfig.slots[key]" />
             </label>
           </div>
         </div>
+        <p class="field-hint" style="margin-top: 0.5rem">
+          Your browser's local timezone: <strong>{{ Intl.DateTimeFormat().resolvedOptions().timeZone }}</strong>
+        </p>
       </section>
 
       <!-- RSS Feeds -->
@@ -2697,6 +2731,32 @@ function formatUserDate(iso: string): string {
   flex-wrap: wrap;
   margin-top: 0.5rem;
 }
+.briefing-unit-toggle {
+  display: flex;
+  gap: 0;
+  border: 1px solid var(--color-border);
+  border-radius: 8px;
+  overflow: hidden;
+  width: fit-content;
+  margin-top: 0.25rem;
+}
+.briefing-unit-btn {
+  padding: 0.35rem 1rem;
+  background: var(--color-bg-card);
+  color: var(--color-text-muted);
+  font-size: 0.85rem;
+  cursor: pointer;
+  border: none;
+  font-family: inherit;
+  transition: all 0.15s;
+}
+.briefing-unit-btn:first-child {
+  border-right: 1px solid var(--color-border);
+}
+.briefing-unit-btn.active {
+  background: var(--color-primary);
+  color: #fff;
+}
 .briefing-day-btn {
   padding: 0.35rem 0.65rem;
   border: 1px solid var(--color-border);