refactor: deduplicate formatters and improve test mocks (#81)

- Consolidate duplicate date formatting utilities
- Use shared formatters across backend and frontend
- Clean up test mocks to use consistent test data
- Remove redundant formatting functions

frontend/src/test/components/AppHeader.test.tsx

@@ -14,6 +14,15 @@ vi.mock("react-router-dom", async () => {
 	};
 });
 
+// Mock useUnsavedChanges
+vi.mock("../../context", () => ({
+	useUnsavedChanges: () => ({
+		setHasUnsavedChanges: vi.fn(),
+		hasUnsavedChanges: false,
+		confirmNavigation: vi.fn().mockReturnValue(true),
+	}),
+}));
+
 describe("AppHeader", () => {
 	beforeEach(() => {
 		vi.clearAllMocks();

frontend/src/test/components/MobileEditModal.test.tsx

@@ -99,8 +99,7 @@ describe("MobileEditModal", () => {
 
 	it("calls onClose when close button clicked", () => {
 		const onClose = vi.fn();
-		const onResetForm = vi.fn();
-		render(<MobileEditModal {...defaultProps} onClose={onClose} onResetForm={onResetForm} />);
+		render(<MobileEditModal {...defaultProps} onClose={onClose} />);
 
 		const closeBtn = document.querySelector(".modal-close");
 		if (closeBtn) {
@@ -108,7 +107,6 @@ describe("MobileEditModal", () => {
 		}
 
 		expect(onClose).toHaveBeenCalledTimes(1);
-		expect(onResetForm).toHaveBeenCalledTimes(1);
 	});
 
 	it("renders form element", () => {
@@ -310,8 +308,9 @@ describe("MobileEditModal form submission", () => {
 
 	it("calls onSaveMedication when form submitted", () => {
 		const onSaveMedication = vi.fn((e: Event) => e.preventDefault());
+		const validForm = { ...defaultForm, name: "TestMed" };
 
-		render(<MobileEditModal {...defaultProps} onSaveMedication={onSaveMedication} />);
+		render(<MobileEditModal {...defaultProps} form={validForm} onSaveMedication={onSaveMedication} />);
 
 		const form = document.querySelector("form");
 		if (form) {