fix(#1): Address code review findings

- Convert ApiResponse to discriminated union for type-safe error handling
- Add HealthStatus type with HealthState literal union
- Make BaseEntity fields readonly for immutability
- Add GlobalExceptionFilter with structured logging
- Add port validation with clear error messages in main.ts
- Improve parseDate to log warnings for invalid dates
- Add comprehensive Button tests (variants, onClick, disabled)
- Add slugify edge case tests (empty, special chars, numbers)
- Create ESLint configs for all packages
- Remove compiled JS files from src directories
- Convert .prettierrc.js to .prettierrc.json

Refs #1

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

apps/web/src/app/page.tsx

@@ -4,9 +4,7 @@ export default function Home() {
   return (
     <main className="flex min-h-screen flex-col items-center justify-center p-24">
       <h1 className="text-4xl font-bold mb-8">Mosaic Stack</h1>
-      <p className="text-lg text-gray-600 mb-8">
-        Welcome to the Mosaic Stack monorepo
-      </p>
+      <p className="text-lg text-gray-600 mb-8">Welcome to the Mosaic Stack monorepo</p>
       <div className="flex gap-4">
         <Button variant="primary">Get Started</Button>
         <Button variant="secondary">Learn More</Button>