[elenav24]

Closes #31
Fixes mobile input zoom and horizontal overflow. All other requirements from the issue were already implemented in #67

Changes

• Prevented iOS auto-zoom on input focus by increasing input/textarea font-size to 16px (below 16px triggers Safari's auto-zoom-on-focus, which wasn't reliably reverting)
• Added maximum-scale=1 to the viewport meta tag as a backstop against zoom
• Disabled horizontal scrolling on the page/container to fix overflow on mobile

Testing

• Verified on mobile Safari that tapping the text input no longer triggers zoom and that the sidebar opens and closes
• Confirmed no horizontal scroll/overflow on small viewport widths of 360 px - 768 px

[Damans227]

looks good, approving. optional: put the 16px on the message box instead of the button so pinch-zoom still works.