feat: replace sankey chart with column-based journey visualization

package.json

@@ -23,7 +23,6 @@
     "class-variance-authority": "^0.7.1",
     "cobe": "^0.6.5",
     "country-flag-icons": "^1.6.4",
-    "d3-sankey": "^0.12.3",
     "d3-scale": "^4.0.2",
     "framer-motion": "^12.23.26",
     "html-to-image": "^1.11.13",
@@ -52,7 +51,6 @@
     "@tailwindcss/typography": "^0.5.19",
     "@testing-library/jest-dom": "^6.9.1",
     "@testing-library/react": "^16.3.2",
-    "@types/d3-sankey": "^0.12.5",
     "@types/d3-scale": "^4.0.9",
     "@types/node": "^20.14.12",
     "@types/react": "^19.2.14",