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/1974/worldcup.stadiums.json

@@ -0,0 +1,36 @@
+{
+  "stadiums": [
+    {
+      "name": "Olympiastadion",
+      "city": "Munich"
+    },
+    {
+      "name": "Volksparkstadion",
+      "city": "Hamburg"
+    },
+    {
+      "name": "Waldstadion",
+      "city": "Frankfurt"
+    },
+    {
+      "name": "Westfalenstadion",
+      "city": "Dortmund"
+    },
+    {
+      "name": "Parkstadion",
+      "city": "Gelsenkirchen"
+    },
+    {
+      "name": "Niedersachsenstadion",
+      "city": "Hanover"
+    },
+    {
+      "name": "Rheinstadion",
+      "city": "Düsseldorf"
+    },
+    {
+      "name": "Neckarstadion",
+      "city": "Stuttgart"
+    }
+  ]
+}