chore: add Biome for lint and fix all lint errors

- Install @biomejs/biome as devDependency at root
- Configure biome.json with 2-space indent, double quotes, Tailwind CSS support
- Add lint/lint:fix/format/format:fix scripts to root and app package.json
- Fix noNonNullAssertion: env vars extracted to variables with suppression, <div role=button> replaced with <button>
- Fix noUnusedVariables: remove unused destructured vars
- Fix useIterableCallbackReturn: arrow functions with block body
- Fix noExplicitAny: recharts Tooltip formatters
- Fix noLabelWithoutControl: add htmlFor+id or use <span> for non-input labels
- Fix noStaticElementInteractions/useKeyWithClickEvents: role+keyboard events for overlays
- Fix noArrayIndexKey: use error string as key
- Fix CSS parse: enable tailwindDirectives parser
- Normalize formatting across 80 files with biome check --write

apps/backend/prisma/seed.ts

@@ -1,10 +1,13 @@
 import "dotenv/config";
+import { PrismaPg } from "@prisma/adapter-pg";
 import { betterAuth } from "better-auth";
 import { prismaAdapter } from "better-auth/adapters/prisma";
 import { PrismaClient } from "../src/generated/prisma/client";
-import { PrismaPg } from "@prisma/adapter-pg";
 
-const adapter = new PrismaPg({ connectionString: process.env.DATABASE_URL! });
+const adapter = new PrismaPg({
+  // biome-ignore lint/style/noNonNullAssertion: required env var
+  connectionString: process.env.DATABASE_URL!,
+});
 const prisma = new PrismaClient({ adapter });
 
 async function main() {
@@ -26,6 +29,7 @@ async function main() {
       disableSignUp: false,
       minPasswordLength: 4,
     },
+    // biome-ignore lint/style/noNonNullAssertion: required env var
     secret: process.env.BETTER_AUTH_SECRET!,
     baseURL: process.env.BETTER_AUTH_URL ?? "http://localhost:3000",
   });