Set search input font-size to 16px to avoid mobile zoom

iOS Safari auto-zooms when focusing inputs with font-size < 16px.
Setting both the header search box and modal search input to 16px
prevents this unwanted zoom behavior.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Refs #15

Transcript to this point of search: https://gistpreview.github.io/?74c4a80b8e0a00d0904c2a2c17ebe8ff/index.html