style: unify all views on Mission Control V2 design tokens

- Map legacy v1 CSS variables (--nx-*, --panel, --text-*, --surface*) to V2 tokens in nexus-tokens.css
- Restyle global shell (main.css), AppSidebar, AppHeader to match V2 Sidebar/Topbar (glass, gradients, Space Grotesk)
- Add GalaxyBackground to the v1 shell in App.vue
- Replace hardcoded v1 hex colors with V2 tokens in all deviating views (Agents, Calendar, Docs, Incidents, Memory, Notifications, ProjectDetail, Security, Team, TaskDetail, Settings)
- Keep JS status colors as hex where alpha suffixes are concatenated (AgentsIndex, Team, Notifications)
- Add Settings nav item (System group) + gear icon to V2 sidebar so it shows on the dashboard
- No component or layout structure changes; LoginView and TaskBoardView untouched

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

frontend/src/App.vue

@@ -6,6 +6,7 @@ import { useOperationsStore } from './stores/operations'
 import { useAuthStore } from './stores/auth'
 import AppSidebar from './components/layout/AppSidebar.vue'
 import AppHeader from './components/layout/AppHeader.vue'
+import GalaxyBackground from './components/background/GalaxyBackground.vue'
 import ModuleView from './components/ModuleView.vue'
 import ToastContainer from './components/ui/ToastContainer.vue'
 
@@ -46,6 +47,7 @@ onMounted(() => {
 <template>
   <RouterView v-if="route.name === 'Login' || route.name === 'Dashboard'" />
   <div v-else class="shell">
+    <GalaxyBackground />
     <AppSidebar
       :active-view="activeView"
       :mobile-nav-open="mobileNavOpen"
@@ -103,6 +105,8 @@ main {
   display: flex;
   flex-direction: column;
   min-width: 0;
+  position: relative;
+  z-index: 1;
 }
 
 .content {