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/ui/src/components/Button.test.tsx

@@ -1,5 +1,5 @@
-import { describe, expect, it, afterEach } from "vitest";
-import { render, screen, cleanup } from "@testing-library/react";
+import { describe, expect, it, afterEach, vi } from "vitest";
+import { render, screen, cleanup, fireEvent } from "@testing-library/react";
 import { Button } from "./Button.js";
 
 afterEach(() => {
@@ -12,20 +12,75 @@ describe("Button", () => {
     expect(screen.getByRole("button")).toHaveTextContent("Click me");
   });
 
-  it("should apply variant styles", () => {
-    render(<Button variant="danger">Delete</Button>);
-    const button = screen.getByRole("button");
-    expect(button.className).toContain("bg-red-600");
+  describe("variants", () => {
+    it("should apply primary variant styles by default", () => {
+      render(<Button>Primary</Button>);
+      const button = screen.getByRole("button");
+      expect(button.className).toContain("bg-blue-600");
+    });
+
+    it("should apply secondary variant styles", () => {
+      render(<Button variant="secondary">Secondary</Button>);
+      const button = screen.getByRole("button");
+      expect(button.className).toContain("bg-gray-200");
+    });
+
+    it("should apply danger variant styles", () => {
+      render(<Button variant="danger">Delete</Button>);
+      const button = screen.getByRole("button");
+      expect(button.className).toContain("bg-red-600");
+    });
   });
 
-  it("should apply size styles", () => {
-    render(<Button size="lg">Large Button</Button>);
-    const button = screen.getByRole("button");
-    expect(button.className).toContain("px-6");
+  describe("sizes", () => {
+    it("should apply medium size by default", () => {
+      render(<Button>Medium</Button>);
+      const button = screen.getByRole("button");
+      expect(button.className).toContain("px-4");
+    });
+
+    it("should apply small size styles", () => {
+      render(<Button size="sm">Small</Button>);
+      const button = screen.getByRole("button");
+      expect(button.className).toContain("px-3");
+    });
+
+    it("should apply large size styles", () => {
+      render(<Button size="lg">Large Button</Button>);
+      const button = screen.getByRole("button");
+      expect(button.className).toContain("px-6");
+    });
+  });
+
+  describe("onClick", () => {
+    it("should call onClick handler when clicked", () => {
+      const handleClick = vi.fn();
+      render(<Button onClick={handleClick}>Click me</Button>);
+      fireEvent.click(screen.getByRole("button"));
+      expect(handleClick).toHaveBeenCalledTimes(1);
+    });
+
+    it("should not call onClick when disabled", () => {
+      const handleClick = vi.fn();
+      render(
+        <Button onClick={handleClick} disabled>
+          Disabled
+        </Button>
+      );
+      fireEvent.click(screen.getByRole("button"));
+      expect(handleClick).not.toHaveBeenCalled();
+    });
   });
 
   it("should pass through additional props", () => {
     render(<Button disabled>Disabled</Button>);
     expect(screen.getByRole("button")).toBeDisabled();
   });
+
+  it("should merge custom className with default styles", () => {
+    render(<Button className="custom-class">Custom</Button>);
+    const button = screen.getByRole("button");
+    expect(button.className).toContain("custom-class");
+    expect(button.className).toContain("bg-blue-600");
+  });
 });