Form inputs in AddContact and RecipientStep lack associated label elements

[abayomicornelius]

In src/components/ContactBook/AddContact.tsx, the name and address <input> elements only have a placeholder attribute, with no <label htmlFor>, aria-label, or aria-labelledby. The same pattern appears in src/components/SendFlow/RecipientStep.tsx's <textarea>.

Placeholder text disappears on input and isn't reliably exposed to screen readers as a field name, so these forms fail basic WCAG labeling requirements. Add visually-hidden <label>s (the codebase already has VisuallyHidden.tsx for exactly this purpose).