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/api/src/main.ts

@@ -1,17 +1,61 @@
 import { NestFactory } from "@nestjs/core";
 import { AppModule } from "./app.module";
+import { GlobalExceptionFilter } from "./filters/global-exception.filter";
+
+function getPort(): number {
+  const portEnv = process.env.PORT;
+
+  if (portEnv === undefined || portEnv === "") {
+    return 3001;
+  }
+
+  const port = parseInt(portEnv, 10);
+
+  if (isNaN(port)) {
+    throw new Error(`Invalid PORT environment variable: "${portEnv}". PORT must be a number.`);
+  }
+
+  if (port < 1 || port > 65535) {
+    throw new Error(
+      `Invalid PORT environment variable: ${String(port)}. PORT must be between 1 and 65535.`
+    );
+  }
+
+  return port;
+}
 
 async function bootstrap() {
   const app = await NestFactory.create(AppModule);
+
+  app.useGlobalFilters(new GlobalExceptionFilter());
   app.enableCors();
 
-  const port = process.env["PORT"] ?? 3001;
+  const port = getPort();
   await app.listen(port);
 
-  console.log(`API running on http://localhost:${port}`);
+  console.log(`API running on http://localhost:${String(port)}`);
 }
 
 bootstrap().catch((err: unknown) => {
-  console.error("Failed to start application:", err);
+  const isProduction = process.env.NODE_ENV === "production";
+  const errorMessage = err instanceof Error ? err.message : String(err);
+  const errorStack = err instanceof Error ? err.stack : undefined;
+
+  if (isProduction) {
+    console.error(
+      JSON.stringify({
+        level: "error",
+        message: "Failed to start application",
+        error: errorMessage,
+        timestamp: new Date().toISOString(),
+      })
+    );
+  } else {
+    console.error("Failed to start application:", errorMessage);
+    if (errorStack) {
+      console.error(errorStack);
+    }
+  }
+
   process.exit(1);
 });