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>

packages/shared/src/utils/index.test.ts

@@ -35,6 +35,38 @@ describe("slugify", () => {
   it("should trim leading and trailing hyphens", () => {
     expect(slugify("  Hello World  ")).toBe("hello-world");
   });
+
+  it("should handle empty string", () => {
+    expect(slugify("")).toBe("");
+  });
+
+  it("should handle string with only whitespace", () => {
+    expect(slugify("   ")).toBe("");
+  });
+
+  it("should handle consecutive special characters", () => {
+    expect(slugify("Hello---World")).toBe("hello-world");
+    expect(slugify("Hello___World")).toBe("hello-world");
+    expect(slugify("Hello   World")).toBe("hello-world");
+  });
+
+  it("should handle numbers", () => {
+    expect(slugify("Product 123")).toBe("product-123");
+    expect(slugify("2024 New Year")).toBe("2024-new-year");
+  });
+
+  it("should handle mixed case", () => {
+    expect(slugify("HeLLo WoRLd")).toBe("hello-world");
+  });
+
+  it("should remove leading/trailing special chars", () => {
+    expect(slugify("---Hello World---")).toBe("hello-world");
+    expect(slugify("!@#Hello World!@#")).toBe("hello-world");
+  });
+
+  it("should handle string with only special characters", () => {
+    expect(slugify("!@#$%^&*()")).toBe("");
+  });
 });
 
 describe("sleep", () => {