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>

package.json

@@ -31,11 +31,6 @@
     "@hookform/resolvers": "^3.9.1",
     "@mantine/core": "^8.3.13",
     "@mantine/hooks": "^8.3.13",
-    "@nivo/bar": "^0.99.0",
-    "@nivo/core": "^0.99.0",
-    "@nivo/line": "^0.99.0",
-    "@nivo/pie": "^0.99.0",
-    "@nivo/scatterplot": "^0.99.0",
     "@notionhq/client": "^2.3.0",
     "@prisma/client": "^6.19.2",
     "@radix-ui/react-alert-dialog": "^1.1.4",
@@ -57,9 +52,9 @@
     "@radix-ui/react-tabs": "^1.1.2",
     "@radix-ui/react-toggle": "^1.1.10",
     "@radix-ui/react-tooltip": "^1.1.6",
-    "@react-spring/web": "^10.0.3",
     "@tailwindcss/postcss": "^4.1.18",
     "@tanstack/react-query": "^5.62.0",
+    "@tremor/react": "^3.18.7",
     "@trpc/client": "^11.0.0-rc.678",
     "@trpc/react-query": "^11.0.0-rc.678",
     "@trpc/server": "^11.0.0-rc.678",