Replace remaining hardcoded hex colors with color tokens (CR-27)

Map leftover component hex values onto the existing color scale, and leave third-party share brands and the Avatar white-alpha border documented as intentional exceptions.

tests/unit/Step.test.jsx

@@ -150,7 +150,7 @@ describe("Step Component", () => {
     render(<Step {...defaultProps} />);
 
     const textElement = screen.getByText("Test Card Text");
-    expect(textElement).toHaveClass("text-[#141414]");
+    expect(textElement).toHaveClass("text-[var(--color-gray-900)]");
   });
 
   it("handles long text content gracefully", () => {