feat: replace emoji icons with Heroicons SVG set

Install @heroicons/react and replace all emoji usage across stats, history,
search, and team pages with proper SVG icons (outline style, w-3 to w-4).
SectionTitle in stats page refactored to accept an icon component prop.

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

package.json

@@ -16,6 +16,7 @@
   "dependencies": {
     "@apollo/client": "^4.2.3",
     "@graphql-tools/schema": "^10.0.33",
+    "@heroicons/react": "^2.2.0",
     "drizzle-orm": "^0.45.2",
     "flag-icons": "^7.5.0",
     "graphql": "^16.14.2",