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/app.controller.ts

@@ -1,11 +1,7 @@
 import { Controller, Get } from "@nestjs/common";
 import { AppService } from "./app.service";
-import type { ApiResponse } from "@mosaic/shared";
-
-interface HealthStatus {
-  status: string;
-  timestamp: string;
-}
+import type { ApiResponse, HealthStatus } from "@mosaic/shared";
+import { successResponse } from "@mosaic/shared";
 
 @Controller()
 export class AppController {
@@ -18,12 +14,9 @@ export class AppController {
 
   @Get("health")
   getHealth(): ApiResponse<HealthStatus> {
-    return {
-      success: true,
-      data: {
-        status: "healthy",
-        timestamp: new Date().toISOString(),
-      },
-    };
+    return successResponse({
+      status: "healthy",
+      timestamp: new Date().toISOString(),
+    });
   }
 }