chore: setup TypeScript 6 and pnpm with mise

- Add mise.toml with pnpm latest
- Create root workspace with pnpm-workspace.yaml
- Upgrade TypeScript from 5.9.3 to 6.0.3 in apps/web
- Add vite-env.d.ts for CSS module type declarations
- Switch from npm to pnpm package management

apps/web/package.json

@@ -10,14 +10,16 @@
     "typecheck": "tsc --noEmit"
   },
   "dependencies": {
+    "katex": "^0.16.45",
     "lucide-preact": "^1.14.0",
+    "mermaid": "^11.14.0",
     "preact": "^10.27.2",
     "preact-iso": "^2.9.3"
   },
   "devDependencies": {
     "@preact/preset-vite": "^2.10.2",
     "prettier": "^3.6.2",
-    "typescript": "^5.9.3",
+    "typescript": "^6.0.3",
     "vite": "^7.1.12"
   }
 }