feat: replace MUI X Charts Pro with d3-sankey custom Sankey

Remove paid MUI dependency. Use d3-sankey (MIT, ~5KB) for layout
algorithm + custom SVG rendering. Same visual quality: smooth bezier
ribbon links, proper node spacing via sankeyJustify, label backgrounds,
hover dimming, exit nodes.

package.json

@@ -14,10 +14,6 @@
   "dependencies": {
     "@ciphera-net/ui": "^0.2.5",
     "@ducanh2912/next-pwa": "^10.2.9",
-    "@emotion/react": "^11.14.0",
-    "@emotion/styled": "^11.14.1",
-    "@mui/material": "^7.3.9",
-    "@mui/x-charts-pro": "^8.27.5",
     "@phosphor-icons/react": "^2.1.10",
     "@simplewebauthn/browser": "^13.2.2",
     "@stripe/react-stripe-js": "^5.6.0",
@@ -27,6 +23,7 @@
     "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",
@@ -55,6 +52,7 @@
     "@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",