refactor(frontend): deduplicate CSS keyframes, unify types, extract format utils, add UI states, trim mock data

- Remove duplicate @keyframes pulse-* from 3 component files (already in nexus-tokens.css)
- Rename AgentDetail → AgentDetailData in dashboard types to avoid collision with types/agent.ts
- Extract shared formatNumber/initials/formatTime to utils/format.ts
- Simplify FlowBoard: use agentStore modal/selection getters instead of duplicating local state
- Add error banner + empty state to IrisChat; add loading skeleton + error/empty states to TaskStrip
- Remove 105-line unused mockAgents array from useFlowLayout
- Reduce operations store fallbacks from hardcoded preview data to minimal safe defaults
- Update operations store tests to match lean fallback structure
- Net: -73 lines, cleaner imports, fewer magic strings

frontend/src/components/layout/Sidebar.vue

@@ -7,6 +7,7 @@ import { useTaskStore } from '../../stores/tasks'
 import { navigation, icons } from '../../composables/icons'
 import type { NavGroupDef } from '../../composables/icons'
 import NavGroup from './NavGroup.vue'
+import { initials } from '../../utils/format'
 
 const auth = useAuthStore()
 const router = useRouter()
@@ -14,8 +15,7 @@ const agentStore = useAgentStore()
 const taskStore = useTaskStore()
 
 const ownerInitials = computed(() =>
-  auth.user?.displayName?.split(' ').map(p => p[0]).join('').slice(0, 2).toUpperCase()
-  ?? 'OW'
+  auth.user?.displayName ? initials(auth.user.displayName) : 'OW'
 )
 
 function logout() {