docs: screenshots and mobile menu

[adamTrz]

Summary

Fixes the issues reported in the Slack thread against the Rspress/Callstack-themed React Native Paper docs.

• Restores the current-root legacy TextInput screenshots so the existing 5.x TextInput, TextInput.Affix, and TextInput.Icon screenshot references render instead of broken image icons.
• Fixes the mobile docs menu duplicate hamburger by hiding the redundant pseudo-icon when the theme already renders an SVG icon.
• Makes the version selector dropdown use an opaque background and positions it below the sticky docs menu on mobile docs pages.
• Updates the home banner Let's talk CTA from the stale /contact-us URL to the live /contact URL.

[satya164]

thanks