Add comprehensive test coverage for Share component error handling

[Copilot]

The Share component's error handling logic (handleShare function with callbacks, state management, setTimeout behavior) lacked test coverage despite other components having extensive tests (ErrorBoundary: 397 lines, utils.error-handling: 328 lines).

Changes

Added 25 tests covering:

• State transitions: isSharing, shareStatus updates, aria-disabled attribute
• Callback behavior: onSuccess/onError invocations with correct parameters
• Timeout mechanics: 3s success timeout, 5s error timeout, cleanup on unmount, timeout replacement on rapid clicks
• Accessibility: ARIA role attributes (alert for errors, status for success), aria-live="polite"
• Styling: Success/error message colors
• Edge cases: Multiple rapid clicks, unmount during timeout

Test patterns

Used vitest with real timers for timeout tests to avoid fake timer complexity with React async updates:

test("success message clears after timeout", async () => {
  mockShareHandler.mockImplementation(async ({ onSuccess }) => {
    onSuccess("Link copied to clipboard");
  });

  fireEvent.click(link);
  await waitFor(() => {
    expect(container.querySelector(".share-status.success")).toBeTruthy();
  });

  await new Promise(resolve => setTimeout(resolve, 3100));
  expect(container.querySelector(".share-status")).toBeFalsy();
}, 10000);

All 25 tests pass. No security vulnerabilities (CodeQL).

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