feat: daily briefing frontend — view, setup wizard, settings tab, nav

- BriefingView: soft chat UI with conversation history dropdown, SSE
  streaming via chat store, manual refresh trigger, today/past conv toggle
- BriefingSetupWizard: 4-step first-time setup overlay (welcome →
  locations → office days → RSS feeds)
- SettingsView: Briefing tab with enable toggle, location geocoding,
  office day picker, slot toggles, RSS feed management, notifications
- AppHeader + router: /briefing route and nav link (desktop + mobile)
- client.ts: briefing types and API functions (config, feeds, convs,
  geocode, trigger)

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

frontend/src/components/AppHeader.vue

@@ -77,6 +77,7 @@ router.afterEach(() => {
         <router-link to="/tasks" class="nav-link">Tasks</router-link>
         <router-link to="/chat" :class="['nav-link', { 'router-link-active': isChatActive }]">Chat</router-link>
         <router-link to="/graph" class="nav-link">Graph</router-link>
+        <router-link to="/briefing" class="nav-link">Briefing</router-link>
         <router-link to="/shared" class="nav-link">Shared</router-link>
       </div>
 
@@ -125,6 +126,7 @@ router.afterEach(() => {
       <router-link to="/tasks" class="nav-link">Tasks</router-link>
       <router-link to="/chat" :class="['nav-link', { 'router-link-active': isChatActive }]">Chat</router-link>
       <router-link to="/graph" class="nav-link">Graph</router-link>
+      <router-link to="/briefing" class="nav-link">Briefing</router-link>
       <router-link to="/shared" class="nav-link">Shared</router-link>
       <div class="mobile-divider"></div>
       <router-link to="/settings" class="nav-link">Settings</router-link>