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>

.gitignore

@@ -7,6 +7,16 @@ dist
 .next
 .turbo
 
+# Compiled source (prevent accidental commits)
+apps/*/src/**/*.js
+apps/*/src/**/*.d.ts
+apps/*/src/**/*.js.map
+apps/*/src/**/*.d.ts.map
+packages/*/src/**/*.js
+packages/*/src/**/*.d.ts
+packages/*/src/**/*.js.map
+packages/*/src/**/*.d.ts.map
+
 # IDE
 .idea
 .vscode