Fix: contact form labels and social links #71

Follow-up to #66. The contact fields only have placeholders, and some social links still go to platform homepages.

client/src/pages/Contact.tsx and client/src/components/Footer.tsx

• Add visible labels for name, email and message, with suitable autocomplete values.
• Confirm UMSA’s social accounts and update the contact/footer links. Remove any unconfirmed accounts.
• Check the form and long email address fit on mobile.