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/components/layouts/observer-nav.tsx

@@ -1,6 +1,6 @@
 'use client'
 
-import { BarChart3, Home } from 'lucide-react'
+import { BarChart3, Home, FolderKanban } from 'lucide-react'
 import { RoleNav, type NavItem, type RoleNavUser } from '@/components/layouts/role-nav'
 
 interface ObserverNavProps {
@@ -14,6 +14,11 @@ export function ObserverNav({ user }: ObserverNavProps) {
       href: '/observer',
       icon: Home,
     },
+    {
+      name: 'Projects',
+      href: '/observer/projects',
+      icon: FolderKanban,
+    },
     {
       name: 'Reports',
       href: '/observer/reports',