Dark themes:
- Midnight: ultra-minimal, near-black, zero effects
- Hacker: green-on-black terminal, monospace, CRT scanlines
- Neon: hot pink + cyan on purple-black, synthwave, heavy glow
Light themes:
- Paper: warm cream/sepia, serif fonts, book-like
- Arctic: cool whites and icy blues, crisp and modern
- Solarized: Ethan Schoonover's solarized-light palette
Theme picker:
- Replaced simple dark/light toggle with grouped dropdown
- Themes organized by Dark / Light sections with active checkmark
- Remembers last dark and light theme separately for quick toggle
- Theme metadata now includes variant field for proper grouping
- Custom themes default to dark variant
