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/router/index.ts

@@ -110,6 +110,11 @@ const router = createRouter({
       name: "shared-with-me",
       component: () => import("@/views/SharedWithMeView.vue"),
     },
+    {
+      path: "/briefing",
+      name: "briefing",
+      component: () => import("@/views/BriefingView.vue"),
+    },
     {
       path: "/settings",
       name: "settings",