Observer platform redesign Phase 4: migrate charts to Tremor, redesign all pages

- Migrate 9 chart components from Nivo to @tremor/react (BarChart, AreaChart, DonutChart, ScatterChart)
- Remove @nivo/*, @react-spring/web dependencies (45 packages removed)
- Redesign dashboard: 6 stat tiles, competition pipeline, score distribution, juror workload, activity feed
- Add new /observer/projects page with search, filters, sorting, pagination, CSV export
- Restructure reports page from 5 tabs to 3 (Progress, Jurors, Scores & Analytics) with per-tab CSV export
- Redesign project detail: breadcrumb nav, score card header, 3-tab layout (Overview/Evaluations/Files)
- Update loading skeletons to match new layouts

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

src/app/(observer)/observer/loading.tsx

@@ -0,0 +1,88 @@
+import { Skeleton } from '@/components/ui/skeleton'
+import { Card, CardContent, CardHeader } from '@/components/ui/card'
+
+export default function ObserverLoading() {
+  return (
+    <div className="space-y-6">
+      {/* Header */}
+      <div className="flex items-center justify-between">
+        <div>
+          <Skeleton className="h-8 w-48" />
+          <Skeleton className="mt-2 h-4 w-32" />
+        </div>
+        <Skeleton className="h-10 w-[200px]" />
+      </div>
+
+      {/* 6 stat tiles */}
+      <div className="grid gap-4 grid-cols-2 md:grid-cols-3 lg:grid-cols-6">
+        {[...Array(6)].map((_, i) => (
+          <Card key={i}>
+            <CardContent className="p-4">
+              <div className="space-y-2">
+                <Skeleton className="h-4 w-16" />
+                <Skeleton className="h-8 w-12" />
+                <Skeleton className="h-3 w-20" />
+              </div>
+            </CardContent>
+          </Card>
+        ))}
+      </div>
+
+      {/* Pipeline */}
+      <Card>
+        <CardHeader>
+          <Skeleton className="h-5 w-32" />
+        </CardHeader>
+        <CardContent>
+          <div className="flex gap-4 overflow-hidden">
+            {[...Array(4)].map((_, i) => (
+              <Skeleton key={i} className="h-24 w-48 shrink-0 rounded-lg" />
+            ))}
+          </div>
+        </CardContent>
+      </Card>
+
+      {/* 3-col middle row */}
+      <div className="grid gap-4 lg:grid-cols-3">
+        {[...Array(3)].map((_, i) => (
+          <Card key={i}>
+            <CardHeader>
+              <Skeleton className="h-5 w-28" />
+            </CardHeader>
+            <CardContent>
+              <Skeleton className="h-[200px] w-full" />
+            </CardContent>
+          </Card>
+        ))}
+      </div>
+
+      {/* 2-col bottom row */}
+      <div className="grid gap-4 lg:grid-cols-2">
+        <Card>
+          <CardHeader>
+            <Skeleton className="h-5 w-32" />
+          </CardHeader>
+          <CardContent className="space-y-2">
+            {[...Array(5)].map((_, i) => (
+              <Skeleton key={i} className="h-10 w-full" />
+            ))}
+          </CardContent>
+        </Card>
+        <Card>
+          <CardHeader>
+            <Skeleton className="h-5 w-28" />
+          </CardHeader>
+          <CardContent className="space-y-3">
+            {[...Array(5)].map((_, i) => (
+              <div key={i} className="flex items-center gap-3">
+                <Skeleton className="h-3 w-3 rounded-full" />
+                <Skeleton className="h-4 flex-1" />
+                <Skeleton className="h-3 w-16" />
+              </div>
+            ))}
+          </CardContent>
+        </Card>
+      </div>
+    </div>
+  )
+}