Add more color themes (Solarized, Dracula, Catppuccin)

[turqoisehex]

Summary

Screen Break ships with 3 themes (dark, light, nord) defined in the THEMES dict at line ~802 of screen_break.py. Adding popular editor themes would give users more personalization options.

Acceptance Criteria

• Add at least 2 new themes (e.g., Solarized Dark, Dracula, Catppuccin Mocha)
• Each theme defines: bg, card, card_in, accent, accent2, text, text_dim, green, red
• New themes appear in the Settings dropdown automatically
• Test that all overlay windows render correctly with new colors

Relevant Code

• THEMES dict: screen_break.py line ~802
• apply_theme(): screen_break.py line ~832
• Color variables: C_BG, C_CARD, C_ACCENT, etc. (line ~766)

Notes

Adding a theme is straightforward: copy an existing entry in the THEMES dict and change the color values. The apply_theme() function handles applying colors globally. This is a good first issue because it requires no architectural changes -- just adding data to an existing dict.