refactor: dashboard design critique — eliminate redundancy, differentiate sections

- Remove GreetingStatStrip (duplicated PerformanceCards data)
- Strip left-border accent from stat cards (AI slop pattern)
- Redesign KnowledgeBaseCards: icon grid → compact row list with icon badges
- Redesign TeamSummary: distinct inline-row layout, no longer identical twin
- Differentiate hover: stat cards use subtle border-hover, sessions keep springy lift
- Add loading skeletons to PerformanceCards, KnowledgeBaseCards, TeamSummary
- Add error state to PerformanceCards
- Extract timeAgo() to shared lib/timeAgo.ts (replaced 4 duplicates)
- Fix Skeleton bg-brand-border (undefined CSS var) → border-default
- Fix double text-xs text-[0.5625rem] class conflicts across dashboard

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/pages/QuickStartPage.tsx

@@ -6,7 +6,6 @@ import { ActiveFlowPilotSessions } from '@/components/dashboard/ActiveFlowPilotS
 import { PerformanceCards } from '@/components/dashboard/PerformanceCards'
 import { KnowledgeBaseCards } from '@/components/dashboard/KnowledgeBaseCards'
 import { TeamSummary } from '@/components/dashboard/TeamSummary'
-import { GreetingStatStrip } from '@/components/dashboard/GreetingStatStrip'
 
 function SectionLabel({ children, action }: { children: React.ReactNode; action?: React.ReactNode }) {
   return (
@@ -37,18 +36,14 @@ export function QuickStartPage() {
     <div className="overflow-y-auto h-full">
       <PageMeta title="ResolutionFlow" />
       <div className="max-w-4xl mx-auto px-6 pt-12 pb-12">
-        {/* Hero: Greeting + Stat Strip */}
-        <div className="flex items-end justify-between mb-8 animate-fade-in-up">
-          <div>
-            <p className="font-sans text-xs uppercase tracking-[0.12em] text-muted-foreground mb-1">
-              {dayOfWeek}, {formattedDate}
-            </p>
-            <h1 className="font-heading text-3xl sm:text-4xl font-extrabold tracking-tight text-[#f0f2f5] leading-tight">
-              Good {greeting},<br className="hidden sm:block" />
-              {firstName}.
-            </h1>
-          </div>
-          <GreetingStatStrip />
+        {/* Hero: Greeting */}
+        <div className="mb-8 animate-fade-in-up">
+          <p className="font-sans text-xs uppercase tracking-[0.12em] text-muted-foreground mb-1">
+            {dayOfWeek}, {formattedDate}
+          </p>
+          <h1 className="font-heading text-3xl sm:text-4xl font-extrabold tracking-tight text-[#f0f2f5] leading-tight">
+            Good {greeting}, {firstName}.
+          </h1>
         </div>
 
         {/* Chat-style input */}