Expand themes collection to ~60 themes (litmus-jr2u)

Add ~30 new well-known themes from verified sources: GitHub, One Light, Night Owl, Iceberg, Snazzy, Zenburn, Flexoki, Oxocarbon, Poimandres, Cyberdream, Vesper, Modus, Nightfox family, Sonokai, Andromeda, Melange, Tender

Summary of Changes

Added 31 new themes from well-known, verified sources (official repos, kitty-themes, alacritty-theme, iTerm2-Color-Schemes):

New theme families (with dark/light variants):

• GitHub (Dark, Light, Dark Dimmed) — from projekt0n/github-theme-contrib
• Cyberdream (Dark, Light) — from scottmckendry/cyberdream.nvim
• Flexoki (Dark, Light) — from kepano/flexoki
• Iceberg (Dark, Light) — from cocopon/iceberg.vim
• Melange (Dark, Light) — from savq/melange-nvim
• Modus (Vivendi, Operandi) — from GNU Emacs modus-themes
• Night Owl + Light Owl — from sdras/night-owl-vscode-theme
• Oxocarbon (Dark, Light) — from nyoom-engineering/oxocarbon
• Sonokai (Default, Shusia) — from sainnhe/sonokai

New Nightfox family members:

• Dawnfox, Dayfox, Duskfox, Nordfox, Terafox — from EdenEast/nightfox.nvim
• Moved existing nightfox.toml into nightfox/ directory

New standalone themes:

• Andromeda — from EliverLara/Andromeda
• One Light — Atom One Light terminal port
• Poimandres — from drcmda/poimandres-theme
• Snazzy — from sindresorhus/hyper-snazzy
• Tender — from jacoborus/tender.vim
• Vesper — from raunofreiberg/vesper
• Zenburn — classic vim theme

Code changes:

• Updated themes.rs with 60 include_str! entries (was 29)
• Updated family.rs with new prefix families + suffix-based grouping for Nightfox and Owl families
• All tests pass

Total: 29 → 60 themes