refactor: replace hardcoded hex colors with theme tokens, move data/ to root

- Add --color-green-mid token (#4a7a55) to @theme for dimmer stat values
- Replace all text-[#hex]/bg-[#hex] arbitrary values with named tokens:
  text-green, text-green-light, text-green-sec, text-green-muted,
  text-green-dark, text-green-mid, text-text, bg-card, bg-bg, border-border
- Replace rgba(34,197,94,X) inline styles with bg-green/X opacity modifiers
- Convert single-prop style={{ borderColor/background }} to className
- Fix SVG stroke="#dff5e8" → stroke="currentColor"
- Use CSS variables in globals.css base styles (background-color, color)
- Move app/data/wikipedia/ → data/ (project root, not inside Next.js app dir)
- Update Dockerfile, seed.ts, scrape-wikipedia.ts paths accordingly
- Remove unused app/data/world_cup.csv

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

data/1990/worldcup.stadiums.json

@@ -0,0 +1,56 @@
+{
+  "stadiums": [
+    {
+      "name": "Stadio San Paolo",
+      "city": "Naples"
+    },
+    {
+      "name": "Stadio San Nicola",
+      "city": "Bari"
+    },
+    {
+      "name": "Stadio Delle Alpi",
+      "city": "Turin"
+    },
+    {
+      "name": "San Siro",
+      "city": "Milan"
+    },
+    {
+      "name": "Stadio Luigi Ferraris",
+      "city": "Genoa"
+    },
+    {
+      "name": "Stadio Olimpico",
+      "city": "Rome"
+    },
+    {
+      "name": "Stadio Marc'Antonio Bentegodi",
+      "city": "Verona"
+    },
+    {
+      "name": "Stadio Renato Dall'Ara",
+      "city": "Bologna"
+    },
+    {
+      "name": "Stadio Comunale",
+      "city": "Florence"
+    },
+    {
+      "name": "Stadio delle Alpi",
+      "city": "Turin"
+    },
+    {
+      "name": "Stadio Friuli",
+      "city": "Udine"
+    },
+    {
+      "name": "Stadio Sant'Elia",
+      "city": "Cagliari"
+    },
+    {
+      "name": "Stadio La Favorita",
+      "city": "Palermo"
+    }
+  ]
+}