Adds three new color themes alongside the existing Stalwart/Ocean/
Forest/Violet set so more people can find one they like, and switches
the out-of-the-box defaults to Ocean + square corners instead of the
neutral Stalwart theme + rounded corners (existing users' saved
preferences are untouched, this only changes what a fresh install
starts with).
Verified in the browser: all three new themes render with legible
primary-foreground contrast in both light and dark mode, and the
pre-hydration flash-prevention script in main.tsx (which reads
localStorage before React mounts) now recognizes the new theme names.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
